rpi3: drop -O0 flag for ARM-TF

Drops the -O0 flag passed in CFLAGS when compiling ARM-TF. This is
needed to ensure that the binaries doesn't overflow their assigned
memory.

Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>

rpi3.mk

@@ -56,7 +56,6 @@ clean: arm-tf-clean busybox-clean u-boot-clean u-boot-rpi-bin-clean \
 # ARM Trusted Firmware
 ################################################################################
 ARM_TF_EXPORTS ?= \
-	CFLAGS="-O0 -gdwarf-2" \
 	CROSS_COMPILE="$(CCACHE)$(AARCH64_CROSS_COMPILE)"
 
 ARM_TF_FLAGS ?= \