Add parameter and it's initialization, needed for hibernation.

Reimplement dwc2_set_param_power_down() to support hibernation too.
Now 'power_down' parameter can be initialized with 0, 1 or 2.
0 - No
1 - Partial power down
2 - Hibernation
Signed-off-by: Vardan Mikayelyan <mvardan@synopsys.com>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Grigor Tovmasyan <tovmasya@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>