KVM: x86/vPMU: Enable PMU handling for AMD PERFCTRn and EVNTSELn MSRs

This patch enables AMD guest VM to access (R/W) PMU related MSRs, which
include PERFCTR[0..3] and EVNTSEL[0..3].

Reviewed-by: Joerg Roedel <jroedel@suse.de>
Tested-by: Joerg Roedel <jroedel@suse.de>
Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wei Huang <wei@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>