x86/CPU: Add native CPUID variants returning a single datum

... similarly to the cpuid_<reg>() variants.

Signed-off-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/20170109114147.5082-2-bp@alien8.de


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>