arm64: Align CMA sizes to PAGE_SIZE

dma_alloc_from_contiguous takes number of pages for a size.
Align up the dma size passed in to page size to avoid truncation
and allocation failures on sizes less than PAGE_SIZE.

Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>