usb: gadget: udc-xilinx: Add clock support

Currently the driver depends on the  bootloader to enable the clocks.
Add support for clocking. The patch enables the clock at  probe and
disables them at remove.

Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Acked-by: Felipe Balbi <balbi@kernel.org>
Link: https://lore.kernel.org/r/054de6deeab81020eaf0399add2839c36b64275f.1632805672.git.shubhrajyoti.datta@xilinx.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>