ARM: OMAP: Move plat-omap/dma-omap.h to include/linux/omap-dma.h

Based on earlier discussions[1] we attempted to find a suitable
location for the omap DMA header in commit 2b6c4e73 (ARM: OMAP:
DMA: Move plat/dma.h to plat-omap/dma-omap.h) until the conversion
to dmaengine is complete.

Unfortunately that was before I was able to try to test compile
of the ARM multiplatform builds for omap2+, and the end result
was not very good.

So I'm creating yet another all over the place patch to cut the
last dependency for building omap2+ for ARM multiplatform. After
this, we have finally removed the driver dependencies to the
arch/arm code, except for few drivers that are being worked on.

The other option was to make the <plat-omap/dma-omap.h> path
to work, but we'd have to add some new header directory to for
multiplatform builds.

Or we would have to manually include arch/arm/plat-omap/include
again from arch/arm/Makefile for omap2+.

Neither of these alternatives sound appealing as they will
likely lead additio...