arc: Implement arch-specific dma_map_ops.mmap

We used to use generic implementation of dma_map_ops.mmap which is
dma_common_mmap() but that only worked for simpler cached mappings when
vaddr = paddr.

If a driver requests uncached DMA buffer kernel maps it to virtual
address so that MMU gets involved and page uncached status takes into
account. In that case usage of dma_common_mmap() lead to mapping of
vaddr to vaddr for user-space which is obviously wrong. For more detals
please refer to verbose explanation here [1].

So here we implement our own version of mmap() which always deals
with dma_addr and maps underlying memory to user-space properly
(note that DMA buffer mapped to user-space is always uncached
because there's no way to properly manage cache from user-space).

[1] https://lkml.org/lkml/2016/10/26/973

Reviewed-by: Catalin Marinas <[email protected]>
Cc: Marek Szyprowski <[email protected]>
Cc: <[email protected]>  #4.5+
Signed-off-by: Alexey Brodkin <[email protected]>
Signed-off-by: Vineet Gupta <[email protected]>

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