x86/cpu: Merge Intel and AMD ppin_init() functions

The code to decide whether a system supports the PPIN (Protected
Processor Inventory Number) MSR was cloned from the Intel
implementation. Apart from the X86_FEATURE bit and the MSR numbers it is
identical.

Merge the two functions into common x86 code, but use x86_match_cpu()
instead of the switch (c->x86_model) that was used by the old Intel
code.

No functional change.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220131230111.2004669-2-tony.luck@intel.com