ARM: OMAP: Remove __REG access in DMA code

ARM: OMAP: Remove __REG access in DMA code

Remove __REG access in DMA code, use dma_read/write instead:

- dynamically set the omap_dma_base based on the omap type

- omap_read/write becomes dma_read/write
- dma channel registers are read with dma_ch_read/write

Signed-off-by: Tony Lindgren <tony@atomide.com>