common: DMA-mapping: add DMA_ATTR_FORCE_CONTIGUOUS attribute

This patch adds DMA_ATTR_FORCE_CONTIGUOUS attribute to the DMA-mapping
subsystem.

By default DMA-mapping subsystem is allowed to assemble the buffer
allocated by dma_alloc_attrs() function from individual pages if it can
be mapped as contiguous chunk into device dma address space. By
specifing this attribute the allocated buffer is forced to be contiguous
also in physical memory.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>