xen/arm: p2m: Don't need to restore the state for an idle vCPU.

The function p2m_restore_state could be called with an idle vCPU in
arguments (when called by construct_dom0). However, we will never return
to EL0/EL1 in this case, so it is not necessary to restore the p2m
registers.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

xen/arch/arm/p2m.c

@@ -127,6 +127,9 @@ void p2m_restore_state(struct vcpu *n)
 {
     register_t hcr;
 
+    if ( is_idle_vcpu(n) )
+        return;
+
     hcr = READ_SYSREG(HCR_EL2);
     WRITE_SYSREG(hcr & ~HCR_VM, HCR_EL2);
     isb();