spi: Migrate CONFIG_KIRKWOOD_SPI to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/configs/ds109_defconfig b/configs/ds109_defconfig
index c4d76c1..ec41ab7 100644
--- a/configs/ds109_defconfig
+++ b/configs/ds109_defconfig
@@ -21,6 +21,7 @@
 CONFIG_SPI_FLASH_BAR=y
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_SYS_NS16550=y
+CONFIG_KIRKWOOD_SPI=y
 CONFIG_USB=y
 CONFIG_USB_EHCI_HCD=y
 CONFIG_FS_EXT4=y