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/smartweb_defconfig b/configs/smartweb_defconfig
index c6743d4..a81e2e5 100644
--- a/configs/smartweb_defconfig
+++ b/configs/smartweb_defconfig
@@ -9,6 +9,7 @@
 CONFIG_SYS_EXTRA_OPTIONS="AT91SAM9260"
 CONFIG_BOOTDELAY=3
 CONFIG_SPL=y
+CONFIG_SPL_NAND_SUPPORT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="U-Boot# "
 CONFIG_AUTOBOOT_KEYED=y