ARM: 8527/1: virt: enable GICv3 system registers

ARMv8 introduces system registers for the Generic Interrupt Controllers
CPU and virtual interfaces.  When GICv3 is implemented, EL2 needs to
allow the kernel to use those registers, by changing the value of
ICC_HSRE.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>