tools/x86/kcpuid: Extend CPUID index mask macro

tools/x86/kcpuid: Extend CPUID index mask macro

Extend the CPUID index mask macro from 0x80000000 to 0xffff0000.  This
accommodates the Transmeta (0x80860000) and Centaur (0xc0000000) index
ranges which will be later added.

This also automatically sets CPUID_FUNCTION_MASK to 0x0000ffff, which is
the actual correct value.  Use that macro, instead of the 0xffff literal
where appropriate.

Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20250324142042.29010-13-darwi@linutronix.de