KVM: SVM: fix compilation with modular PSP and non-modular KVM

Use svm_sev_enabled() in order to cull all calls to PSP code.  Otherwise,
compilation fails with undefined symbols if the PSP device driver is compiled
as a module and KVM is not.
Reported-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/sev.c

@@ -1117,7 +1117,7 @@ int __init sev_hardware_setup(void)
 	/* Maximum number of encrypted guests supported simultaneously */
 	max_sev_asid = cpuid_ecx(0x8000001F);
 
-	if (!max_sev_asid)
+	if (!svm_sev_enabled())
 		return 1;
 
 	/* Minimum ASID value that should be used for SEV guest */
@@ -1156,6 +1156,9 @@ int __init sev_hardware_setup(void)
 
 void sev_hardware_teardown(void)
 {
+	if (!svm_sev_enabled())
+		return;
+
 	bitmap_free(sev_asid_bitmap);
 	bitmap_free(sev_reclaim_asid_bitmap);