usb: dwc2: use u32 for DT binding parameters

Commit 05ee799f ("usb: dwc2: Move gadget settings into core_params")
changes to type u16 for DT binding "g-rx-fifo-size" and
"g-np-tx-fifo-size" but use type u32 for "g-tx-fifo-size". Finally the
the first two parameters cannot be passed successfully with wrong data
format. This is found the data transferring broken on 96boards Hikey.

This patch is to change all parameters to u32 type, and verified on
Hikey board the DT parameters can pass successfully.

[johnyoun: minor rebase]

Signed-off-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>