usb : musb : Adding DM6446 (TI DaVinci) platform specific USB support

Adding DM6446 (TI DaVinci) platform specific USB functionality for
USB Phy and VBUS initialization.

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>