KVM: selftests: Disallow "get supported CPUID" before REQ_XCOMP_GUEST_PERM

KVM: selftests: Disallow "get supported CPUID" before REQ_XCOMP_GUEST_PERM

Disallow using kvm_get_supported_cpuid() and thus caching KVM's supported
CPUID info before enabling XSAVE-managed features that are off-by-default
and must be enabled by ARCH_REQ_XCOMP_GUEST_PERM.  Caching the supported
CPUID before all XSAVE features are enabled can result in false negatives
due to testing features that were cached before they were enabled.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20221128225735.3291648-4-seanjc@google.com