x86/vpmu: Move vpmu_do_cpuid() handling into {pv,hvm}_cpuid()

x86/vpmu: Move vpmu_do_cpuid() handling into {pv,hvm}_cpuid()

This reduces the net complexity of CPUID handling by having all adjustments in
the same place.  Remove the now-unused vpmu_do_cpuid() infrastructure.

This involves introducing a vpmu_enabled() predicate, and making the Intel
specific VPMU_CPU_HAS_* constants public.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>