spi: Migrate CONFIG_MXC_SPI to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/configs/pcm058_defconfig b/configs/pcm058_defconfig
index 2a174ff..14626c3 100644
--- a/configs/pcm058_defconfig
+++ b/configs/pcm058_defconfig
@@ -56,5 +56,6 @@
 CONFIG_PHY_MICREL=y
 CONFIG_PHY_MICREL_KSZ90X1=y
 CONFIG_NETDEVICES=y
+CONFIG_MXC_SPI=y
 CONFIG_DM_THERMAL=y
 CONFIG_OF_LIBFDT=y