spi: Migrate CONFIG_CF_SPI to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/configs/M54418TWR_nand_mii_defconfig b/configs/M54418TWR_nand_mii_defconfig
index cf01533..5b54de3 100644
--- a/configs/M54418TWR_nand_mii_defconfig
+++ b/configs/M54418TWR_nand_mii_defconfig
@@ -19,3 +19,4 @@
 CONFIG_CMD_CACHE=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_ATMEL=y
+CONFIG_CF_SPI=y