arm64: Replace ZONE_DMA32 with ZONE_DMA

On arm64 we do not have two DMA zones, so it does not make sense to
implement ZONE_DMA32. This patch changes ZONE_DMA32 with ZONE_DMA, the
latter covering 32-bit dma address space to honour GFP_DMA allocations.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Git-commit: 19e7640d1f2302c20df2733e3e3df49acb17189e
[joonwoop@codeaurora.org: fixed trivial merge conflict.]
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>