ARM: dts: OMAP4: add *reg* property for ocp2scp

*reg* property for ocp2scp was previously obtained from ti,hwmods property.
But that is now explicitly added to the dt node.
Also updated the documentation with *reg* info.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Benoit Cousson <b-cousson@ti.com>