KVM: arm/arm64: Unify 32bit fault injection

Both arm and arm64 implementations are capable of injecting
faults, and yet have completely divergent implementations,
leading to different bugs and reduced maintainability.

Let's elect the arm64 version as the canonical one
and move it into aarch32.c, which is common to both
architectures.

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