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/a4m2k_defconfig b/configs/a4m2k_defconfig
index ef1c6e5..e688efe 100644
--- a/configs/a4m2k_defconfig
+++ b/configs/a4m2k_defconfig
@@ -9,6 +9,7 @@
 CONFIG_SYS_EXTRA_OPTIONS="A4M2K"
 CONFIG_BOOTDELAY=3
 CONFIG_SPL=y
+CONFIG_SPL_NOR_SUPPORT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_LOOPW=y
 # CONFIG_CMD_SETEXPR is not set