UPSTREAM: usb: dwc2: Move register save and restore functions

UPSTREAM: usb: dwc2: Move register save and restore functions

Move the register save and restore functions into the host and gadget
specific files.

Change-Id: If9a11b19ee459d0cd1cd560f0302c83518b3f6af
Tested-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Huang, Tao <huangtao@rock-chips.com>
(cherry picked from commit 58e52ff6a6c3ce964c71b2dd9f06be426f993524)