ARM: dts: omap4+: Add DMM bindings

Add Dynamic Memory Manager (DMM) bindings for OMAP4 and OMAP5 and DRA7x devices.
DMM only requires address and irq information.

Add documentation for the DMM bindings.

Originally worked on by Andy Gross <andygro@gmail.com>

Cc: Andy Gross <andygro@gmail.com>
Signed-off-by: Archit Taneja <archit@ti.com>
Signed-off-by: Benoit Cousson <bcousson@baylibre.com>