KVM: selftests: Add helpers for safe and safe+forced RDMSR, RDPMC, and XGETBV

Add helpers for safe and safe-with-forced-emulations versions of RDMSR,
RDPMC, and XGETBV.  Use macro shenanigans to eliminate the rather large
amount of boilerplate needed to get values in and out of registers.

Tested-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://lore.kernel.org/r/20240109230250.424295-29-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>