usb: composite: force gadget to be USB2 for HS only function

If one of functions is not super speed capable, we need force the udc
to be high speed, this is an equivalent implementation of
usb_gadget_udc_set_speed() in kernel but simple, which set the gadget
max_speed to be high speed, so afterwards when start gadget duc can
set the HW to be USB 2.0 mode.

Reviewed-by: Ye Li <ye.li@nxp.com>
Reviewed-by: Peter Chen <peter.chen@nxp.com>
Tested-by: faqiang.zhu <faqiang.zhu@nxp.com>
Signed-off-by: Li Jun <jun.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>