usb: dwc3: msm: Remove last of dwc3_otg

The usb_phy structure embedded in dwc3_otg was only needed
to keep track of the host/peripheral states. Add a state
variable to dwc3_msm for the same effect.
The dwc3->dotg pointer is really indicating whether or not
device supports dual-role, so replace it with a simple boolean,
and remove the dwc3_otg_init/exit() functions.
Now we can finally remove what's left of dwc3_otg.h entirely.

Change-Id: Iee86503b876cc8912c9bbacbf778ea398ed7ec20
Signed-off-by: Jack Pham <jackp@codeaurora.org>
Signed-off-by: Azhar Shaikh <azhars@codeaurora.org>