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/a3m071_defconfig b/configs/a3m071_defconfig
index cfb4ca4..67f59ab 100644
--- a/configs/a3m071_defconfig
+++ b/configs/a3m071_defconfig
@@ -8,6 +8,7 @@
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_BOOTDELAY=3
 CONFIG_SPL=y
+CONFIG_SPL_NOR_SUPPORT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_LOOPW=y
 # CONFIG_CMD_SETEXPR is not set