x86/cpufeatures: Correct LKGS feature flag description

x86/cpufeatures: Correct LKGS feature flag description

Quotation marks in cpufeatures.h comments are special and when the
comment begins with a quoted string, that string lands in /proc/cpuinfo,
turning it into a user-visible one.

The LKGS comment doesn't begin with a quoted string but just in case
drop the quoted "kernel" in there to avoid confusion. And while at it,
simply change the description into what the LKGS instruction does for
more clarity.

No functional changes.

Reviewed-by: Xin Li (Intel) <xin@zytor.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20251015103548.10194-1-bp@kernel.org