dma-mapping: benchmark: Add support for multi-pages map/unmap

Currently it only support one page map/unmap once a time for dma-map
benchmark, but there are some other scenaries which need to support for
multi-page map/unmap: for those multi-pages interfaces such as
dma_alloc_coherent() and dma_map_sg(), the time spent on multi-pages
map/unmap is not the time of a single page * npages (not linear) as it
may use block description instead of page description when it is satified
with the size such as 2M/1G, and also it can send a single TLB invalidation
command to invalidate multi-pages instead of multi-times when RIL is
enabled (which will short the time of unmap). So it is necessary to add
support for multi-pages map/unmap.

Add a parameter "-g" to support multi-pages map/unmap.

Signed-off-by: Xiang Chen <chenxiang66@hisilicon.com>
Acked-by: Barry Song <song.bao.hua@hisilicon.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>