KVM: selftests: Add functional test for Intel's fixed PMU counters

Extend the fixed counters test to verify that supported counters can
actually be enabled in the control MSRs, that unsupported counters cannot,
and that enabled counters actually count.

Co-developed-by: Like Xu <likexu@tencent.com>
Signed-off-by: Like Xu <likexu@tencent.com>
Signed-off-by: Jinrong Liang <cloudliang@tencent.com>
[sean: fold into the rd/wr access test, massage changelog]
Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Tested-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://lore.kernel.org/r/20240109230250.424295-21-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>