arm64: KVM: add trap handlers for AArch64 debug registers

arm64: KVM: add trap handlers for AArch64 debug registers

Add handlers for all the AArch64 debug registers that are accessible
from EL0 or EL1. The trapping code keeps track of the state of the
debug registers, allowing for the switch code to implement a lazy
switching strategy.

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>
(cherry picked from commit 0c557ed4983b7abe152212b5b1726c2a789b2c61)
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>