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/releases/coreboot-4.22-relnotes.md

@@ -11,7 +11,7 @@ releases, this one reflects a commitment to open source innovation,
 security enhancements, and expanding hardware support.
 
 
-### 4.22.01 release
+## 4.22.01 release
 
 The week between tagging a release and announcing it publicly is used
 to test the tagged version and make sure everything is working as we
@@ -22,7 +22,7 @@ For the 4.22 release cycle we found an uninitialized variable error on
 the sandybridge/ivybridge platforms and rolled that into the 4.22.01
 release package.
 
-### coreboot version naming update
+## coreboot version naming update
 
 This release is the last release to use the incrementing 4.xx release
 name scheme. For future releases, coreboot is switching to a
@@ -33,7 +33,7 @@ the 24.02 release, we'll append the values .01, .02 and so on to the
 initial release value.
 
 
-### coreboot default branch update
+## coreboot default branch update
 
 Immediately after the 4.21 release, the coreboot project changed the
 default git branch from 'master' to 'main'. For the first couple of