tools/x86/kcpuid: Use <cpuid.h> intrinsics

tools/x86/kcpuid: Use <cpuid.h> intrinsics

Use the __cpuid_count() intrinsic, provided by GCC and LLVM, instead of
rolling a manual version.  Both of the kernel's minimum required GCC
version (5.1) and LLVM version (13.0.1) supports it, and it is heavily
used across standard Linux user-space tooling.

This also makes the CPUID call sites more readable.

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/20250324142042.29010-11-darwi@linutronix.de