usb: dwc2: Add host partial power down functions

usb: dwc2: Add host partial power down functions

For host mode Partial Power Down entering and exiting
separate functions are needed to implement the logic.
Earlier the logic was implemented in one function. Which was
confusing the readability. Also both host and device implementations
were in the same function.

- Added host partial power down functions which must be called
by dwc2_enter_partial_power_down()/dwc2_exit_partial_power_down()
functions.

Added function names:
dwc2_host_enter_partial_power_down()
dwc2_host_exit_partial_power_down()

NOTE: There is a checkpatch "CHECK" warning on "udelay(100)".
The delay is needed to properly exit gadget Partial Power Down
A delay less than 100 doesn't work.

Acked-by: Minas Harutyunyan <Minas.Harutyunyan@synopsys.com>
Signed-off-by: Artur Petrosyan <Arthur.Petrosyan@synopsys.com>
Link: https://lore.kernel.org/r/20210408094438.56CFBA022E@mailhost.synopsys.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>