usb: dwc3: otg: Call dwc3_set_mode() directly

Get rid of dwc3_otg_set_peripheral_regs() and
dwc3_otg_set_host_regs() and simply call dwc3_set_mode()
directly. This reduces duplicated code and performs
additional sequences that had been added more recently,
such as configuring GFLADJ/SOFITPSYNC for host mode, and
setting GUSB3PIPECTL_SUSPHY to allow PHY to enter suspend.

Change-Id: Ib2347442b3dac95609d5b81b9b5e96847609fded
Signed-off-by: Jack Pham <jackp@codeaurora.org>