x86/platform: Improve MSR permission handling for XENPF_resource_op

x86/platform: Improve MSR permission handling for XENPF_resource_op

The logic to disallow writes to the TSC is out-of-place, and should be in
check_resource_access() rather than in resource_access().

Split the existing allow_access_msr() into two - msr_{read,write}_allowed() -
and move all permissions checks here.

Furthermore, guard access to MSR_IA32_CMT_{EVTSEL,CTR} to prohibit their use
on hardware which is lacking the QoS Monitoring feature.  Introduce
cpu_has_pqe to help with the logic.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>