KVM: nSVM: Disable PMU MSR interception as appropriate while running L2

KVM: nSVM: Disable PMU MSR interception as appropriate while running L2

Add MSRs that might be passed through to L1 when running with a mediated
PMU to the nested SVM's set of to-be-merged MSR indices, i.e. disable
interception of PMU MSRs when running L2 if both KVM (L0) and L1 disable
interception.  There is no need for KVM to interpose on such MSR accesses,
e.g. if L1 exposes a mediated PMU (or equivalent) to L2.

Tested-by: Xudong Hao <xudong.hao@intel.com>
Tested-by: Manali Shukla <manali.shukla@amd.com>
Link: https://patch.msgid.link/20251206001720.468579-33-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>