arm64: Use swiotlb late initialisation

Since arm64 does not support ISA, there is no need for early swiotlb
initialisation. This patch switches the DMA mapping code to
swiotlb_tlb_late_init_with_default_size(). A side effect of this is that
GFP_DMA is used for the swiotlb buffer and devices with a 32-bit
coherent mask are correctly supported.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>