usb: musb: OMAP4430: Power down the PHY during board init

Powerdown the internal PHY during board init for OMAP44xx.
So that when musb is disabled core transition to retention/off
is not blocked.

Signed-off-by: Hema HK <hemahk@ti.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>