KVM: SVM: Make KVM_AMD depend on CPU_SUP_AMD or CPU_SUP_HYGON

KVM: SVM: Make KVM_AMD depend on CPU_SUP_AMD or CPU_SUP_HYGON

Make building KVM SVM support depend on support for AMD or Hygon.  KVM
already effectively restricts SVM support to AMD and Hygon by virtue of
the vendor string checks in cpu_has_svm(), and KVM VMX supports depends
on one of its three known vendors (Intel, Centaur, or Zhaoxin).

Add the CPU_SUP_HYGON clause even though CPU_SUP_HYGON selects CPU_SUP_AMD
to document that KVM SVM support isn't just for AMD CPUs, and to prevent
breakage should Hygon support ever become a standalone thing.

Link: https://lore.kernel.org/r/20230721201859.2307736-12-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>