staging: vchiq_arm: Usa a DMA pool for small bulks
During a bulk transfer we request a DMA allocation to hold the
scatter-gather list. Most of the time, this allocation is small
(<< PAGE_SIZE), however it can be requested at a high enough frequency
to cause fragmentation and/or stress the CMA allocator (think time
spent in compaction here, or during allocations elsewhere).
Implement a pool to serve up small DMA allocations, falling back
to a coherent allocation if the request is greater than
VCHIQ_DMA_POOL_SIZE.
Signed-off-by: Oliver Gjoneski <ogjoneski@gmail.com>