usb: dwc2: Add enter partial power down when port is suspended

usb: dwc2: Add enter partial power down when port is suspended

Adds flow of entering Partial Power Down in
"dwc2_port_suspend()" function when core receives suspend.

NOTE: Switch case statement is used for hibernation partial
power down and clock gating mode determination. In this patch
only Partial Power Down is implemented the Hibernation and
clock gating implementations are planned to be added.

Acked-by: Minas Harutyunyan <Minas.Harutyunyan@synopsys.com>
Signed-off-by: Artur Petrosyan <Arthur.Petrosyan@synopsys.com>
Link: https://lore.kernel.org/r/20210408094510.6C4E9A022E@mailhost.synopsys.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>