usb: otg: Adding twl6030-usb transceiver driver for OMAP4430

Adding the twl6030-usb transceiver support for OMAP4 musb driver.

OMAP4 supports 2 types of transceiver interface.

1. UTMI: The PHY is embedded within OMAP4. The transceiver functionality
is split between the twl6030 PMIC chip and OMAP4430. The VBUS, ID pin
sensing and OTG SRP generation part is integrated in TWL6030 and UTMI PHY
functionality is embedded within the OMAP4430.

There is no direct interactions between the MUSB controller and TWL6030
chip to communicate the session-valid, session-end and ID-GND events.
It has to be done through a software by setting/resetting bits in
one of the control module register of OMAP4430 which in turn toggles
the appropriate signals to MUSB controller.

The internal transceiver has functional clocks and
powerdown bits to powerdown the PHY for power saving.

Since there is no option available for having 2 transceiver drivers
for one USB controller, internal PHY specific APIs are passed through
plaform_data function pointers to use in the twl6030-usb transceiver
driver.

2. ULPI interface is provided for off-chip transceivers.

Signed-off-by: Hema HK <hemahk@ti.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Felipe Balbi <balbi@ti.com>