Convert CONFIG_SPL_LIBGENERIC_SUPPORT to Kconfig

Move this option to Kconfig and tidy up existing uses.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/clearfog_defconfig b/configs/clearfog_defconfig
index 971db02..26e4c06 100644
--- a/configs/clearfog_defconfig
+++ b/configs/clearfog_defconfig
@@ -1,6 +1,7 @@
 CONFIG_ARM=y
 CONFIG_ARCH_MVEBU=y
 CONFIG_SPL_LIBCOMMON_SUPPORT=y
+CONFIG_SPL_LIBGENERIC_SUPPORT=y
 CONFIG_TARGET_CLEARFOG=y
 CONFIG_SPL_I2C_SUPPORT=y
 CONFIG_SPL_LIBDISK_SUPPORT=y