Docs: Fix broken header references

MyST Parser automatically generates label "slugs" for headers which
should be used to reference them from links [1]. These labels are in
"slug-case", i.e. the original header text in lower case separated by
dashes, with punctuation removed. This fixes a few "cross-reference
target not found" warnings.

[1] https://myst-parser.readthedocs.io/en/latest/syntax/optional.html#anchor-slug-structure

Change-Id: Ia6970d03b961bde6d7cd0fa3297f8d84b75d3b34
Signed-off-by: Nicholas Chin <nic.c3.14@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83976
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

Documentation/mainboard/lenovo/Ivy_Bridge_series.md

@@ -82,7 +82,7 @@ It is possible to reduce the Intel ME firmware size to free additional
 space for the `bios` region. This is usually referred to as *cleaning the ME* or
 *stripping the ME*.
 After reducing the Intel ME firmware size you must modify the original IFD,
-[split the resulting coreboot ROM](#splitting-the-coreboot-rom) and then write
+[split the resulting coreboot ROM](#splitting-the-corebootrom) and then write
 each ROM using an [external programmer].
 Have a look at [me_cleaner] for more information.