x86/lib: Fix compiler and kernel-doc warnings

Fix the following W=1 warnings:

arch/x86/lib/cmdline.c:

  - Include <asm/cmdline.h> to fix missing-prototypes warnings.

  - Update comment for __cmdline_find_option_bool to fix a kernel-doc warning.

Signed-off-by: Anuradha Weeraman <anuradha@debian.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230103114725.108431-1-anuradha@debian.org