spi: Migrate CONFIG_CF_SPI to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/configs/M54451EVB_stmicro_defconfig b/configs/M54451EVB_stmicro_defconfig
index 79f38db..f637b45 100644
--- a/configs/M54451EVB_stmicro_defconfig
+++ b/configs/M54451EVB_stmicro_defconfig
@@ -21,3 +21,4 @@
 CONFIG_MTD_NOR_FLASH=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_STMICRO=y
+CONFIG_CF_SPI=y