imx8mq_evk: Enable the USB3.0 host port

Setup USB clock in board codes, and enable the DWC3 XHCI and
PHY drivers to make USB3.0 host port working on i.MX8MQ EVK.

Signed-off-by: Ye Li <ye.li@nxp.com>
Reviewed-by: Patrick Wildt <patrick@blueri.se>