x86/cpufeatures: Remove "AMD" from the comments to the AMD-specific leaf

0x8000001f.EAX is an AMD-specific leaf so there's no need to have "AMD"
in almost every feature's comment. Zap it and make the text more
readable this way.

No functional changes.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20241122210707.12742-1-bp@kernel.org