usb : musb : Adding USB VBUS enable functionality for DM644x DVEVM

Adding USB VBUS enable functionality for DM644x DVEVM (TI DaVinci)
platform.

Signed-off-by: Ravi Babu <ravibabu@ti.com>
Signed-off-by: Swaminathan S <swami.iyer@ti.com>
Signed-off-by: Thomas Abraham <t-abraham@ti.com>
Signed-off-by: Ajay Kumar Gupta <ajay.gupta@ti.com>
Signed-off-by: Remy Bohmer <linux@bohmer.net>