KVM: VMX: Use LEAVE in vmx_do_interrupt_irqoff()

Micro-optimize vmx_do_interrupt_irqoff() by substituting
MOV %RBP,%RSP; POP %RBP instruction sequence with equivalent
LEAVE instruction. GCC compiler does this by default for
a generic tuning and for all modern processors:

DEF_TUNE (X86_TUNE_USE_LEAVE, "use_leave",
	  m_386 | m_CORE_ALL | m_K6_GEODE | m_AMD_MULTIPLE | m_ZHAOXIN
	  | m_TREMONT | m_CORE_HYBRID | m_CORE_ATOM | m_GENERIC)

The new code also saves a couple of bytes, from:

  27:	48 89 ec             	mov    %rbp,%rsp
  2a:	5d                   	pop    %rbp

to:

  27:	c9                   	leave

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lore.kernel.org/r/20250414081131.97374-2-ubizjak@gmail.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/vmx/vmenter.S

@@ -59,8 +59,7 @@
 	 * without the explicit restore, thinks the stack is getting walloped.
 	 * Using an unwind hint is problematic due to x86-64's dynamic alignment.
 	 */
-	mov %_ASM_BP, %_ASM_SP
-	pop %_ASM_BP
+	leave
 	RET
 .endm