OMAP: DMA: Replace read/write macros with functions

Prepare DMA library to get converted into DMA driver using platform
device model and hwmod infrastucture(for omap2+, resource structures
for omap1)

The low level read/write macros are replaced with static inline
functions and register offsets are handled through static register
offset tables mapped through  enumeration constants.

These low level read/write functions along with static register offset
tables will be moved to respective mach-omap dma files in the later
patches of this series.

There are no functionality changes with these changes except change in
logic for handling 16bit registers of OMAP1.

Signed-off-by: G, Manjunath Kondaiah <manjugk@ti.com>
Tested-by: Kevin Hilman <khilman@deeprootsystems.com>
Acked-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>