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 dd65a941 ("arm64:
dma-mapping: clear buffers allocated with FORCE_CONTIGUOUS flag").

Link: http://lkml.kernel.org/r/20180709122019eucas1p2340da484acfcc932537e6014f4fd2c29~-sqTPJKij2939229392eucas1p2j@eucas1p2.samsung.comSigned-off-by: NMarek Szyprowski <m.szyprowski@samsung.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NMichał Nazarewicz <mina86@mina86.com>
Acked-by: NLaura Abbott <labbott@redhat.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Cc: Joonsoo Kim <js1304@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>