mediatek/mt8173: Enable ARM trusted firmware integration

In Chromium OS downstream this was done together with adding the support
for ATF, but unfortunately ATF upstream isn't ready yet. This commit
is a reminder to enable things once ATF caught up.

Change-Id: Id0d6908d906a1e54cdda4f232d572d996d9c556f
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Reviewed-on: https://review.coreboot.org/13968
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/soc/mediatek/mt8173/Kconfig

@@ -6,6 +6,7 @@ config SOC_MEDIATEK_MT8173
 	select ARCH_RAMSTAGE_ARMV8_64
 	select ARCH_ROMSTAGE_ARMV8_64
 	select ARCH_VERSTAGE_ARMV8_64
+	select ARM64_USE_ARM_TRUSTED_FIRMWARE
 	select BOOTBLOCK_CONSOLE
 	select HAVE_UART_SPECIAL
 	select SPI_ATOMIC_SEQUENCING if SPI_FLASH