of: also handle dma-noncoherent in of_dma_is_coherent()

of_dma_is_coherent() currently expects the architecture to be
non-coherent and some devices being coherent getting marked
as such with the dma-coherent devicetree property.

For PowerPC CONFIG_OF_DMA_DEFAULT_COHERENT was added which currently
makes of_dma_is_coherent() always return true but doesn't handle
the case of the architecture being coherent but some devices not.

So modify the function to also check for dma-noncoherent and
set a suitable default return value. If CONFIG_OF_DMA_DEFAULT_COHERENT
is set the value starts with true and finding dma-noncoherent will
set it to false and without CONFIG_OF_DMA_DEFAULT_COHERENT, the
behaviour is reversed.

Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Rob Herring <[email protected]>
Reviewed-by: Guo Ren <[email protected]>
Signed-off-by: Heiko Stuebner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>

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