usb, g_dnl: make iSerialNumber board configurable

usb, g_dnl: make iSerialNumber board configurable

add the possibility to set the iSerialNumber board specific.
Default value for iSerialNumber is 0x0. This value can
changed board specific through the new function
g_dnl_set_serialnumber() which must be called from the
board specific function g_dnl_bind_fixup().

Signed-off-by: Heiko Schocher <[email protected]>
Cc: Marek Vasut <[email protected]>
Cc: Lukasz Majewski <[email protected]>
Cc: Kyungmin Park <[email protected]>
Tested-by: Lukasz Majewski <[email protected]>