usb: gadget: Make g_dnl USB settings common

The g_dnl USB settings for the vendor ID, product ID and manufacturer are
actually common settings that can and should be shared by all the gadgets.

Make them common by renaming them, and convert all the users.

Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>