fvp: use gicv3 legacy mode

ARM-TF has changed its default behavior of GIC, so be able to use
https://github.com/linaro-swg/arm-trusted-firmware/tree/optee_arm-tf_2017-06-22


without making any change in OP-TEE and UEFI etc, we set the value of
FVP_USE_GIC_DRIVER to FVP_GICV3_LEGACY.

Signed-off-by: Guanchao Liang <liang.guanchao@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Tested-by: Joakim Bech <joakim.bech@linaro.org> (FVP)

fvp.mk

@@ -46,6 +46,7 @@ ARM_TF_FLAGS ?= \
 	BL33=$(EDK2_BIN) \
 	DEBUG=0 \
 	ARM_TSP_RAM_LOCATION=tdram \
+	FVP_USE_GIC_DRIVER=FVP_GICV3_LEGACY \
 	PLAT=fvp \
 	SPD=opteed