KVM: SVM: Wrap __svm_sev_es_vcpu_run() with #ifdef CONFIG_KVM_AMD_SEV

Compile (and link) __svm_sev_es_vcpu_run() if and only if SEV support is
actually enabled.  This will allow dropping non-existent 32-bit "support"
from __svm_sev_es_vcpu_run() without causing undue confusion.

Intentionally don't provide a stub (but keep the declaration), as any sane
compiler, even with things like KASAN enabled, should eliminate the call
to __svm_sev_es_vcpu_run() since sev_es_guest() unconditionally returns
"false" if CONFIG_KVM_AMD_SEV=n.

Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20240223204233.3337324-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

arch/x86/kvm/svm/vmenter.S

@@ -291,6 +291,7 @@ SYM_FUNC_START(__svm_vcpu_run)
 
 SYM_FUNC_END(__svm_vcpu_run)
 
+#ifdef CONFIG_KVM_AMD_SEV
 /**
  * __svm_sev_es_vcpu_run - Run a SEV-ES vCPU via a transition to SVM guest mode
  * @svm:	struct vcpu_svm *
@@ -389,3 +390,4 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
 	_ASM_EXTABLE(1b, 3b)
 
 SYM_FUNC_END(__svm_sev_es_vcpu_run)
+#endif /* CONFIG_KVM_AMD_SEV */