arm/arm64: KVM: Inject virtual abort when guest exits on external abort

If we spot a data abort bearing the ESR_EL2.EA bit set, we know that
this is an external abort, and that should be punished by the injection
of an abort.

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