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/core/Kconfig b/drivers/core/Kconfig
index c82b564..788f8b7 100644
--- a/drivers/core/Kconfig
+++ b/drivers/core/Kconfig
@@ -1,3 +1,5 @@
+menu "Generic Driver Options"
+
 config DM
 	bool "Enable Driver Model"
 	help
@@ -102,3 +104,5 @@
 	  debug resource management for a managed device.
 
 	  If you are unsure about this, Say N here.
+
+endmenu