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/i2c/Kconfig b/drivers/i2c/Kconfig
index 9a62ddd..c40bd5c 100644
--- a/drivers/i2c/Kconfig
+++ b/drivers/i2c/Kconfig
@@ -1,3 +1,9 @@
+#
+# I2C subsystem configuration
+#
+
+menu "I2C support"
+
 config DM_I2C
 	bool "Enable Driver Model for I2C drivers"
 	depends on DM
@@ -99,3 +105,5 @@
 	  This I2C controller is used on PH1-Pro4 or newer UniPhier SoCs.
 
 source "drivers/i2c/muxes/Kconfig"
+
+endmenu