KVM: selftests: Track unavailable_mask for PMU events as 32-bit value

KVM: selftests: Track unavailable_mask for PMU events as 32-bit value

Track the mask of "unavailable" PMU events as a 32-bit value.  While bits
31:9 are currently reserved, silently truncating those bits is unnecessary
and asking for missed coverage.  To avoid running afoul of the sanity check
in vcpu_set_cpuid_property(), explicitly adjust the mask based on the
non-reserved bits as reported by KVM's supported CPUID.

Opportunistically update the "all ones" testcase to pass -1u instead of
0xff.

Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Tested-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://lore.kernel.org/r/20250919214648.1585683-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>