usb: dwc2: Improve handling of host and device hwparams

Adds separate functions to get the host and device specific hardware
parameters. The functions check whether the parameters need to be read
at all, depending on dr_mode, and forces the mode only if necessary.
This saves some delays during probe. This also adds two device mode
parameters that will be used by the gadget.

Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>