OMAP at least gets the return type(s) for the DMA translation functions
wrong, which can lead to subtle errors.  Avoid this by moving the DMA
translation functions to asm/dma-mapping.h, and converting them to
inline functions.

Fix the OMAP DMA translation macros to use the correct argument and
result types.

Also, remove the unnecessary casts in dmabounce.c.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>