spi: Migrate CONFIG_MXC_SPI to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/configs/zc5202_defconfig b/configs/zc5202_defconfig
index 82769ad..82e8fc3 100644
--- a/configs/zc5202_defconfig
+++ b/configs/zc5202_defconfig
@@ -31,4 +31,5 @@
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_PCI=y
+CONFIG_MXC_SPI=y
 CONFIG_OF_LIBFDT=y