Documentation: Fix header levels

This fixes the following MyST Parser warnings:

- Non-consecutive header level increase
- Document headings start at H2, not H1

The header levels (the number of "#" characters before a heading) are
intended to form a logical hierarchy of each section and subsection in a
document. A subsection typically should have a header level one more
than its parent section. Most of these warnings are caused by extra "#"
characters, which were simply removed, or sections missing a "#"
character to make it fall under its parent section.

Notable changes:

getting_started/kconfig.md: Changed the header level of the "Keywords"
section from 2 to 3 to fall under "Kconfig Language" (level 2), and
increased the level of each keyword from 3 to 4 to remain under
"Keywords". This also fixes the warnings of "H3 to H5" increases, since
the Usage/Example/Notes/Restrictions sections for each keyword had a
level of 5.

soc/intel/cse_fw_update/cse_fw_update.md: Changed the first line to a
top level header acting as the title of the document. Without this
soc/intel/index.md displays all the level 2 headers in this document
instead of a single link to cse_fw_update.md.

Change-Id: Ia1f8b52e39b7b6524bef89a95365541235b5b1b9
Signed-off-by: Nicholas Chin <nic.c3.14@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83382
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>

Documentation/util/abuild/index.md

@@ -14,7 +14,7 @@ to make sure your patch compiles cleanly for all.
 Note that abuild is a tool to do a simple build test, and binaries it
 produces may well not boot if flashed to a system.
 
-### Basic usage
+## Basic usage
 
 abuild needs to be run from the coreboot directory. If you cd into the
 coreboot/util/abuild directory and try to run it from there, it will
@@ -30,7 +30,7 @@ example, to build the Lenovo X230 target, run:
 $ util/abuild/abuild -t lenovo/x230
 ```
 
-### Where builds and logs are stored
+## Where builds and logs are stored
 
 The resulting images and logs are stored in directory coreboot-builds/
 under your current directory. This can be overridden with --outdir:
@@ -53,7 +53,7 @@ coreboot-builds/passing_boards and coreboot-builds/failing_boards.
 **These logs are overwritten with each abuild run.** Save them elsewhere
 if you feel a need to reference the results later.
 
-### Payloads
+## Payloads
 
 You can also specify a payload directory with -p:
 
@@ -81,7 +81,7 @@ You can also tell abuild not to use a payload:
 util/abuild/abuild -t lenovo/x230 -p none
 ```
 
-### Build non-default configurations
+## Build non-default configurations
 
 Sometimes you do need to build test a custom, non-default configuration.
 This can be accomplished by placing a config file in configs/.
@@ -142,7 +142,7 @@ a file named `myconfig` with this line:
 and run `abuild -K myconfig` to build everything with a silent postcar
 stage.
 
-### Selectively build certain targets only (also config file naming caveats)
+## Selectively build certain targets only (also config file naming caveats)
 
 The P8Z77-M PRO example above would fail for P8Z77-M, because the
 config file name is ambiguous. `abuild` would pick up this config when
@@ -166,7 +166,7 @@ util/abuild/abuild --skip_unset USE_NATIVE_RAMINIT
 This example skips building configs not using (Sandy/Ivy Bridge) native
 RAM init.
 
-### Additional Examples
+## Additional Examples
 
 Many boards have multiple variants. You can build for a specific
 variant of a board:
@@ -203,7 +203,7 @@ Of course, the real power of abuild is in testing multiple boards.
 util/abuild/abuild -B -y -c 8 -p none
 ```
 
-### Full options list
+## Full options list
 
 ```text
 coreboot autobuild v0.11.01 (Feb 3, 2023)