usb: dwc3: make maximum-speed a per-instance attribute

in order to allow different instances of the
core work in different maximum speeds, we will
move the maximum_speed module_parameter to
both DeviceTree (making use the new maximum-speed
DT property) and platform_data.

Signed-off-by: Felipe Balbi <balbi@ti.com>

diff --cc drivers/usb/dwc3/core.c
Simple merge

diff --cc drivers/usb/dwc3/gadget.c
Simple merge

diff --cc drivers/usb/dwc3/platform_data.h
Simple merge