x86/virt: KVM: Open code cpu_has_svm() into kvm_is_svm_supported()

Fold the guts of cpu_has_svm() into kvm_is_svm_supported(), its sole
remaining user.

No functional change intended.

Reviewed-by: Kai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/r/20230721201859.2307736-14-seanjc@google.com


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