ARM: dts: omap4: Update the DSP node

The compatible property for the DSP node is updated to match
the OMAP remoteproc bindings. The node is moved from the soc
node to the ocp node to better reflect the connectivity from
MPU side.

The node is updated with the 'ti,bootreg', 'clocks', 'resets',
'iommus', 'mboxes' and 'firmware' properties. Note that the
node does not have any 'reg' or 'reg-names' properties since
it doesn't have any L2 RAM memory, but only Unicaches.

The node is disabled for now, and should be enabled as per
the individual product configuration in the corresponding
board dts files.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>