Convert CONFIG_SPL_NOR_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/edminiv2_defconfig b/configs/edminiv2_defconfig
index 43e0091..bed6335 100644
--- a/configs/edminiv2_defconfig
+++ b/configs/edminiv2_defconfig
@@ -5,6 +5,7 @@
 CONFIG_TARGET_EDMINIV2=y
 CONFIG_BOOTDELAY=3
 CONFIG_SPL=y
+CONFIG_SPL_NOR_SUPPORT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="EDMiniV2> "
 CONFIG_CMD_I2C=y