Provide the algorithm option to DMA allocators as well, along with
convenience variants for zeroed and aligned memory. The following
four functions are added:

- gen_pool_dma_alloc_algo()
- gen_pool_dma_alloc_align()
- gen_pool_dma_zalloc_algo()
- gen_pool_dma_zalloc_align()
Signed-off-by: Fredrik Noring <noring@nocrew.org>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Christoph Hellwig <hch@lst.de>