spi: Migrate CONFIG_MXC_SPI to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/configs/display5_factory_defconfig b/configs/display5_factory_defconfig
index aac50cc..2ccdfdd 100644
--- a/configs/display5_factory_defconfig
+++ b/configs/display5_factory_defconfig
@@ -66,6 +66,7 @@
 CONFIG_FEC_MXC=y
 # CONFIG_SPL_DM_SERIAL is not set
 CONFIG_MXC_UART=y
+CONFIG_MXC_SPI=y
 CONFIG_USB=y
 CONFIG_USB_GADGET=y
 CONFIG_USB_GADGET_MANUFACTURER="Liebherr"