This patch moves all GICv2 driver files into new added
'gicv2.mk' makefile for the benefit of the generic driver
which can evolve in the future without affecting platforms.

NOTE: Usage of 'drivers/arm/gic/common/gic_common.c' file
is now deprecated and platforms with GICv2 driver need to
be modified to include 'drivers/arm/gic/v2/gicv2.mk' in
their makefiles.

Change-Id: Ib10e71bdda0e5c7e80a049ddce2de1dd839602d1
Signed-off-by: Alexei Fedorov <Alexei.Fedorov@arm.com>