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)