gadget: rockchip: USB_GADGET_PRODUCT_NUM

Rockchip support differnet or common gadget product number
between Rockchip SoCs like,

0x310a - rk3036
0x320a - rk3229, rk3288
0x330a - rk3328

So, select them on Kconfig based on platform specific
config defined.
   
This eventually drop the explicit configs defined in
supporting board defconfig files.

Tested-by: Levin Du <djw@t-chip.com.cn>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>