ARM: dma-mapping: remove redundant code and do the cleanup

This patch just performs a global cleanup in DMA mapping implementation
for ARM architecture. Some of the tiny helper functions have been moved
to the caller code, some have been merged together.

Change-Id: I60b3450bd1180ea007e7326a63762d3a44b3c25d
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Tested-By: Subash Patel <subash.ramaswamy@linaro.org>
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>