KVM: VMX: Use arch_xchg() when processing PIR to avoid instrumentation

Use arch_xchg() when moving IRQs from the PIR to the vIRR, purely to avoid
instrumentation so that KVM is compatible with the needs of posted MSI.
This will allow extracting the core PIR logic to common code and sharing
it between KVM and posted MSI handling.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Sean Christopherson <[e-mail]>

arch/x86/kvm/lapic.c

···
 		if (!pir_vals[i])
 			continue;
 
-		pir_vals[i] = xchg(&pir[i], 0);
+		pir_vals[i] = arch_xchg(&pir[i], 0);
 	}
 
 	for (i = vec = 0; i <= 7; i++, vec += 32) {