arm64: KVM: Inject a Virtual SError if it was pending

If we have caught an SError whilst exiting, we've tagged the
exit code with the pending information. In that case, let's
re-inject the error into the guest, after having adjusted
the PC if required.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>