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/uniphier_ld20_defconfig b/configs/uniphier_ld20_defconfig
index c4a8547..d5f901e 100644
--- a/configs/uniphier_ld20_defconfig
+++ b/configs/uniphier_ld20_defconfig
@@ -4,6 +4,7 @@
 CONFIG_MICRO_SUPPORT_CARD=y
 CONFIG_SYS_TEXT_BASE=0x84000000
 CONFIG_DEFAULT_DEVICE_TREE="uniphier-ph1-ld20-ref"
+CONFIG_SPL_NOR_SUPPORT=y
 CONFIG_HUSH_PARSER=y
 # CONFIG_CMD_XIMG is not set
 # CONFIG_CMD_ENV_EXISTS is not set