usb: otg: Upgrade support for PHY retention mode

Current implementation supports PHY retention mode, when
VBUS detection is done by PMIC.
This change adds the support for PHY retention mode, for
the case where VBUS detection is done by USB PHY.
In that case, the PHY wakes up the MPM and CORE using its
High-Voltage interrupts.

Change-Id: I5fec518337413f175a8bc671897836affc55381c
Signed-off-by: Amit Blay <ablay@codeaurora.org>