KVM: arm64: Add emulation for 32bit guests accessing ACTLR2

ACTLR_EL1 is a 64bit register while the 32bit ACTLR is obviously 32bit.
For 32bit software, the extra bits are accessible via ACTLR2... which
KVM doesn't emulate.

Suggested-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200529150656.7339-3-james.morse@arm.com