ARM: mx3: enable SPI_IMX for better compile coverage

SPI_IMX defaults to m for i.MX machines.  So enabling SPI is enough.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

arch/arm/configs/mx3_defconfig

@@ -84,6 +84,7 @@ CONFIG_SERIAL_IMX_CONSOLE=y
 CONFIG_I2C=y
 CONFIG_I2C_CHARDEV=y
 CONFIG_I2C_IMX=y
+CONFIG_SPI=y
 CONFIG_W1=y
 CONFIG_W1_MASTER_MXC=y
 CONFIG_W1_SLAVE_THERM=y