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

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

Merge KVM's PMU MSR interception bitmaps with those of L1, i.e. merge the
bitmaps of vmcs01 and vmcs12, e.g. so that KVM doesn't interpose on MSR
accesses unnecessarily if L1 exposes a mediated PMU (or equivalent) to L2.

Signed-off-by: Mingwei Zhang <mizhang@google.com>
Co-developed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
[sean: rewrite changelog and comment, omit MSRs that are always intercepted]
Tested-by: Xudong Hao <xudong.hao@intel.com>
Tested-by: Manali Shukla <manali.shukla@amd.com>
Link: https://patch.msgid.link/20251206001720.468579-32-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>