ARM: dts: OMAP4+: Add DMM bindings

Add Dynamic Memory Manager (DMM) bindings for OMAP4 and OMAP5 devices.
Add documentation for the DMM bindings.

Signed-off-by: Andy Gross <andy.gross@ti.com>
ARM: OMAP2+: Don't create DMM if DT present

Added code to conditionally skip over creating a DMM device from the
hwmod information if there is a DMM node present in the DT.

Signed-off-by: Andy Gross <andy.gross@ti.com>