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>

dm: Add Kconfig for driver/demo

Add a suitable Kconfig for this directory.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Masahiro Yamada <yamada.m@jp.panasonic.com>