ARM: imx_v6_v7_defconfig: add CONFIG_I2C_MUX_GPIO

I2C muxing is used on Nitrogen6_MAX board from Boundary Devices.
Signed-off-by: NGary Bisson <gary.bisson@boundarydevices.com>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>

arch/arm/configs/imx_v6_v7_defconfig

@@ -180,6 +180,7 @@ CONFIG_SERIAL_FSL_LPUART=y
 CONFIG_SERIAL_FSL_LPUART_CONSOLE=y
 # CONFIG_I2C_COMPAT is not set
 CONFIG_I2C_CHARDEV=y
+CONFIG_I2C_MUX_GPIO=y
 # CONFIG_I2C_HELPER_AUTO is not set
 CONFIG_I2C_ALGOPCF=m
 CONFIG_I2C_ALGOPCA=m