arm64: KVM: common infrastructure for handling AArch32 CP14/CP15

As we're about to trap a bunch of CP14 registers, let's rework
the CP15 handling so it can be generalized and work with multiple
tables.

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