x86/cpuid: Introduce a centralized CPUID parser

Introduce a CPUID parser for populating the system's CPUID tables.

Since accessing a leaf within the CPUID table requires compile time
tokenization, split the parser into two stages:

  (a) Compile-time macros for tokenizing the leaf/subleaf offsets within
      the CPUID table.

  (b) Generic runtime code to fill the CPUID data, using a parsing table
      which collects these compile-time offsets.

For actual CPUID output parsing, support both generic and leaf-specific
read functions.

To ensure CPUID data early availability, invoke the parser during early
boot, early Xen boot, and at early secondary CPUs bring up.

Provide call site APIs to refresh a single leaf, or a leaf range, within
the CPUID tables.  This is for sites issuing MSR writes that partially
change the CPU's CPUID layout.  Doing full CPUID table rescans in such
cases will be destructive since the CPUID tables will host all of the
kernel's X86_FEATURE flags at a later stage.

Suggested-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/all/20260327021645.555257-1-darwi@linutronix.de

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