xen/PMU: Intercept PMU-related MSR and APIC accesses

xen/PMU: Intercept PMU-related MSR and APIC accesses

Provide interfaces for recognizing accesses to PMU-related MSRs and
LVTPC APIC and process these accesses in Xen PMU code.

(The interrupt handler performs XENPMU_flush right away in the beginning
since no PMU emulation is available. It will be added with a later patch).

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
(cherry picked from commit 6b08cd6328c58a2ae190c5ee03a2ffcab5ef828e)
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>