ARM: dma: Drop __GFP_COMP for iommu dma memory allocations

__iommu_alloc_buffer wants to split pages after allocation in order to
reduce the memory footprint. This does not work well with __GFP_COMP
pages, so drop this flag before allocation

One failure example is snd_malloc_dev_pages call dma_alloc_coherent with
__GFP_COMP.

Signed-off-by: Richard Zhao <rizhao@nvidia.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>