KVM: arm64: Inject AArch32 exceptions from HYP

Similarly to what has been done for AArch64, move the AArch32 exception
injection to HYP.

In order to not use the regmap selection code at EL2, simplify the code
populating the target mode's LR register by useing the compatibility
aliases for LR_abt and LR_und.

We also introduce new accessors for SPSR_abt and SPSR_und, and
move VBAR/SCTLR to using the AArch64 accessors (the use of the AArch32
names was an ARMv7 leftover).

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>