configs/titanium_defconfig: Select MX6

In 21782828 this config wasn't updated by accident, so update it.
Signed-off-by: NTom Rini <trini@konsulko.com>

configs/titanium_defconfig

 CONFIG_ARM=y
+CONFIG_ARCH_MX6=y
 CONFIG_TARGET_TITANIUM=y
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/barco/titanium/imximage.cfg"
 # CONFIG_CMD_IMLS is not set