dma-mapping: replace zone_dma_bits by zone_dma_limit

The hardware DMA limit might not be power of 2. When RAM range starts
above 0, say 4GB, DMA limit of 30 bits should end at 5GB.  A single high
bit can not encode this limit.

Use a plain  address for the DMA zone limit instead.

Since the DMA zone can now potentially span beyond 4GB physical limit of
DMA32, make sure to use DMA zone for GFP_DMA32 allocations in that case.

Signed-off-by: Catalin Marinas <[email protected]>
Co-developed-by: Baruch Siach <[email protected]>
Signed-off-by: Baruch Siach <[email protected]>
Reviewed-by: Catalin Marinas <[email protected]>
Reviewed-by: Petr Tesarik <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>

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