KVM: x86: support CONFIG_KVM_AMD=y with CONFIG_CRYPTO_DEV_CCP_DD=m

SEV requires access to the AMD cryptographic device APIs, and this
does not work when KVM is builtin and the crypto driver is a module.
Actually the Kconfig conditions for CONFIG_KVM_AMD_SEV try to disable
SEV in that case, but it does not work because the actual crypto
calls are not culled, only sev_hardware_setup() is.

This patch adds two CONFIG_KVM_AMD_SEV checks that gate all the remaining
SEV code; it fixes this particular configuration, and drops 5 KiB of
code when CONFIG_KVM_AMD_SEV=n.
Reported-by: NGuenter Roeck <linux@roeck-us.net>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm.c

@@ -436,14 +436,18 @@ static inline struct kvm_svm *to_kvm_svm(struct kvm *kvm)
 
 static inline bool svm_sev_enabled(void)
 {
-	return max_sev_asid;
+	return IS_ENABLED(CONFIG_KVM_AMD_SEV) ? max_sev_asid : 0;
 }
 
 static inline bool sev_guest(struct kvm *kvm)
 {
+#ifdef CONFIG_KVM_AMD_SEV
 	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
 
 	return sev->active;
+#else
+	return false;
+#endif
 }
 
 static inline int sev_get_asid(struct kvm *kvm)