spi: Migrate CONFIG_KIRKWOOD_SPI to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/configs/km_kirkwood_128m16_defconfig b/configs/km_kirkwood_128m16_defconfig
index 9fff51e..96349e1 100644
--- a/configs/km_kirkwood_128m16_defconfig
+++ b/configs/km_kirkwood_128m16_defconfig
@@ -30,5 +30,6 @@
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_SYS_NS16550=y
+CONFIG_KIRKWOOD_SPI=y
 CONFIG_BCH=y
 CONFIG_OF_LIBFDT=y