KVM: SVM: Create a stack frame in __svm_sev_es_vcpu_run()

Now that KVM uses the host save area to context switch RBP, i.e.
preserves RBP for the entirety of __svm_sev_es_vcpu_run(), create a stack
frame using the standared FRAME_{BEGIN,END} macros.

Note, __svm_sev_es_vcpu_run() is subtly not a leaf function as it can call
into ibpb_feature() via UNTRAIN_RET_VM.

Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20240223204233.3337324-8-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/svm/vmenter.S

@@ -3,6 +3,7 @@
 #include <asm/asm.h>
 #include <asm/asm-offsets.h>
 #include <asm/bitsperlong.h>
+#include <asm/frame.h>
 #include <asm/kvm_vcpu_regs.h>
 #include <asm/nospec-branch.h>
 #include "kvm-asm-offsets.h"
@@ -312,6 +313,8 @@ SYM_FUNC_END(__svm_vcpu_run)
  * @spec_ctrl_intercepted: bool
  */
 SYM_FUNC_START(__svm_sev_es_vcpu_run)
+	FRAME_BEGIN
+
 	/*
 	 * Save non-volatile (callee-saved) registers to the host save area.
 	 * Except for RAX and RSP, all GPRs are restored on #VMEXIT, but not
@@ -362,6 +365,7 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
 	 */
 	UNTRAIN_RET_VM
 
+	FRAME_END
 	RET
 
 	RESTORE_GUEST_SPEC_CTRL_BODY