arm-trusted-firmware: Disable a couple of warnings for GCC 6.2

- Remove warnings about code using deprecated declarations such as:
plat/mediatek/mt8173/bl31_plat_setup.c: In function 'bl31_platform_setup':
plat/mediatek/mt8173/bl31_plat_setup.c:175:2: warning:
'arm_gic_setup' is deprecated [-Wdeprecated-declarations]
include/drivers/arm/arm_gic.h:44:6: note: declared here:
void arm_gic_setup(void) __deprecated;

- Disable pedantic warnings to get rid of these warnings:
In file included from plat/mediatek/mt8173/bl31_plat_setup.c:36:0:
plat/mediatek/mt8173/include/mcucfg.h:134:21: error:
enumerator value for 'MP1_CPUCFG_64BIT' is not an integer constant
expression [-Werror=pedantic]
MP1_CPUCFG_64BIT = 0xf << MP1_CPUCFG_64BIT_SHIFT

Change-Id: Ibf2c4972232b2ad743ba689825cfe8440d63e828
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/17995
Tested-by: build bot (Jenkins)
Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/arch/arm64/Makefile.inc

@@ -166,7 +166,7 @@ BL31_MAKEARGS += IS_ANYTHING_TO_BUILD=1
 # multi line string.
 BL31_MAKEARGS += BUILD_MESSAGE_TIMESTAMP='"$(shell grep "\#define COREBOOT_BUILD\>" $(obj)/build.h |cut -d\" -f2 \# \")"'
 
-BL31_CFLAGS := -fno-pic -fno-stack-protector
+BL31_CFLAGS := -fno-pic -fno-stack-protector -Wno-deprecated-declarations
 BL31_LDFLAGS := --emit-relocs
 
 BL31 := $(obj)/bl31.elf
@@ -176,7 +176,7 @@ $(BL31): $(obj)/build.h
 	+CROSS_COMPILE="$(CROSS_COMPILE_arm64)" \
 	CFLAGS="$(BL31_CFLAGS)" \
 	LDFLAGS="$(BL31_LDFLAGS)" \
-	$(MAKE) -C $(BL31_SOURCE) $(BL31_MAKEARGS) $(BL31_TARGET)
+	$(MAKE) -C $(BL31_SOURCE) $(BL31_MAKEARGS) $(BL31_TARGET) DISABLE_PEDANTIC=1
 	mv $(BL31_TARGET) $@
 
 .PHONY: $(BL31)