usb: dwc2: Update enter clock gating when port is suspended

Updates the implementation of entering clock gating mode
when core receives port suspend.
Instead of setting the required bit fields of the registers
inline, called the "dwc2_host_enter_clock_gating()" function.

Signed-off-by: Artur Petrosyan <Arthur.Petrosyan@synopsys.com>
Link: https://lore.kernel.org/r/20210413073653.9F493A0094@mailhost.synopsys.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>