drivers: bus: add a new driver for omap-ocp2scp

Adds a new driver *omap-ocp2scp*. This driver takes the responsibility of
creating all the devices that is connected to OCP2SCP. In the case of OMAP4,
USB2PHY is connected to ocp2scp.

This also includes device tree support for ocp2scp driver and
the documentation with device tree binding information is updated.

Acked-by: Felipe Balbi <balbi@ti.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>