ARM: OMAP: musb: Add ti81xx phy power function

Adding ti81xx_musb_phy_power() which will be used by musb driver through
its function pointer in board_data.

Signed-off-by: Ajay Kumar Gupta <ajay.gupta@ti.com>
Signed-off-by: Ravi Babu <ravibabu@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>