KVM: arm64: vgic-v3: Add ICV_DIR_EL1 handler

Add a handler for writing the guest's view of the ICC_DIR_EL1
register, performing the deactivation of an interrupt if EOImode
is set ot 1.

Tested-by: Alexander Graf <agraf@suse.de>
Acked-by: David Daney <david.daney@cavium.com>
Reviewed-by: Christoffer Dall <cdall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@linaro.org>