dma-buf: Add support for partial cache maintenance

In order to improve performance allow dma-buf clients the ability
to apply cache maintenance to only a subset of a dma-buf.

Kernel clients will be able to use dma_buf_begin_cpu_access_partial
and dma_buf_end_cpu_access_partial functions to only apply cache
maintenance to a range within the dma-buf.

Userspace clients will be able to restrict cache maintenance to only
the subset of the dma-buf which is mmap(ed) by setting the
DMA_BUF_SYNC_USER_MAPPED flag when calling the DMA_BUF_IOCTL_SYNC IOCT.

Change-Id: Id02e240ec43de636bb801929016c8d351b2ae96d
Signed-off-by: Liam Mark <lmark@codeaurora.org>