x86/cpuid: Refactor <asm/cpuid.h>

x86/cpuid: Refactor <asm/cpuid.h>

In preparation for future commits where CPUID headers will be expanded,
refactor the CPUID header <asm/cpuid.h> into:

    asm/cpuid/
    ├── api.h
    └── types.h

Move the CPUID data structures into <asm/cpuid/types.h> and the access
APIs into <asm/cpuid/api.h>.  Let <asm/cpuid.h> be just an include of
<asm/cpuid/api.h> so that existing call sites do not break.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: "Ahmed S. Darwish" <darwi@linutronix.de>
Cc: x86-cpuid@lists.linux.dev
Link: https://lore.kernel.org/r/20250317221824.3738853-2-mingo@kernel.org