drivers: hierarchize drivers Kconfig menu

The menuconfig for drivers are getting more and more cluttered
and unreadable because too many entries are displayed in a single
flat menu.  Use hierarchic menu for each category.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
[trini: Update to apply again in a few places, drop USB hunk]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/demo/Kconfig b/drivers/demo/Kconfig
index 7a8ce18..98bb633 100644
--- a/drivers/demo/Kconfig
+++ b/drivers/demo/Kconfig
@@ -1,3 +1,5 @@
+menu "Demo for driver model"
+
 config DM_DEMO
 	bool "Enable demo uclass support"
 	depends on DM
@@ -24,3 +26,5 @@
 	  a shape when the 'demo hello' command is executed which targets
 	  this device. It can be used to help understand how driver model
 	  works.
+
+endmenu