KVM: SVM: avoid frequency indirect calls

When retpoline is enabled, indirect function calls introduce additional
performance overhead. Avoid frequent indirect calls to VMGEXIT when SEV
is enabled.

Signed-off-by: Peng Hao <flyingpeng@tencent.com>
Link: https://lore.kernel.org/r/20250306075425.66693-1-flyingpeng@tencent.com


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