usb: dwc2: gadget: configure fifos from device tree

As fifo size can vary between SOCs, add possibility to configure
them from device tree. Fifo sizes used by the legacy driver will
be used If they are not provided by the device tree.

Tested-by: Robert Baldyga <r.baldyga@samsung.com>
Acked-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Gregory Herrero <gregory.herrero@intel.com>
Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@intel.com>
Reviewed-by: Robert Baldyga <r.baldyga@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>