usb, g_dnl: make possibility to fixup the device_desc board specific

usb, g_dnl: make possibility to fixup the device_desc board specific

add a weak dummy function g_dnl_fixup to add the possibility to update
the device_desc board specific. Used on the upcoming siemens board
support, where idVendor and idProduct is stored in an eeprom.

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Marek Vasut <marek.vasut@gmail.com>
Cc: Lukasz Majewski <l.majewski@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>