ARM: dts: Add missing dma hwmods property for omap3

On omap3, we are missing a ti,hwmods property for dma that
the SoC interconnect code needs.

Note that this will only show up as a bug with "doesn't have
mpu register target base" boot errors when the legacy platform
data is removed.

Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>