mm/cma: remove unsupported gfp_mask parameter from cma_alloc()

mm/cma: remove unsupported gfp_mask parameter from cma_alloc()

cma_alloc() doesn't really support gfp flags other than __GFP_NOWARN, so
convert gfp_mask parameter to boolean no_warn parameter.

This will help to avoid giving false feeling that this function supports
standard gfp flags and callers can pass __GFP_ZERO to get zeroed buffer,
what has already been an issue: see commit dd65a941f6ba ("arm64:
dma-mapping: clear buffers allocated with FORCE_CONTIGUOUS flag").

Link: http://lkml.kernel.org/r/20180709122019eucas1p2340da484acfcc932537e6014f4fd2c29~-sqTPJKij2939229392eucas1p2j@eucas1p2.samsung.com
Signed-off-by: Marek Szyprowski <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Acked-by: Michał Nazarewicz <[email protected]>
Acked-by: Laura Abbott <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>