Convert CONFIG_SPL_NAND_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/brppt1_nand_defconfig b/configs/brppt1_nand_defconfig
index 67a6acb..a3d7638 100644
--- a/configs/brppt1_nand_defconfig
+++ b/configs/brppt1_nand_defconfig
@@ -9,6 +9,7 @@
 CONFIG_BOOTDELAY=-2
 CONFIG_VERSION_VARIABLE=y
 CONFIG_SPL=y
+CONFIG_SPL_NAND_SUPPORT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMI is not set