usb: otg: TWL6030: Introduce the twl6030_phy_suspend function.

Introduce the twl6030_phy_suspend function and assign to otg.set_suspend
function pointer.
This function is used by the musb-omap2430 platform driver
during suspend/resume.

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>