Add X86_FEATURE_* magic in the style of KVM-Unit-Tests' implementation,
where the CPUID function, index, output register, and output bit position
are embedded in the macro value.  Add kvm_cpu_has() to query KVM's
supported CPUID and use it set_sregs_test, which is the most prolific
user of manual feature querying.

Opportunstically rename calc_cr4_feature_bits() to
calc_supported_cr4_feature_bits() to better capture how the CR4 bits are
chosen.

Link: https://lore.kernel.org/all/20210422005626.564163-1-ricarkol@google.comSuggested-by: Paolo Bonzini <pbonzini@redhat.com>
Suggested-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220614200707.3315957-4-seanjc@google.com