driver core: initialize a default DMA mask for platform device

We still treat devices without a DMA mask as defaulting to 32-bits for
both mask, but a few releases ago we've started warning about such
cases, as they require special cases to work around this sloppyness.
Add a dma_mask field to struct platform_device so that we can initialize
the dma_mask pointer in struct device and initialize both masks to
32-bits by default, replacing similar functionality in m68k and
powerpc.  The arch_setup_pdev_archdata hooks is now unused and removed.

Note that the code looks a little odd with the various conditionals
because we have to support platform_device structures that are
statically allocated.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/20190816062435.881-7-hch@lst.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/m68k/kernel/dma.c

@@ -79,12 +79,3 @@ void arch_sync_dma_for_device(struct device *dev, phys_addr_t handle,
 		break;
 	}
 }
-
-void arch_setup_pdev_archdata(struct platform_device *pdev)
-{
-	if (pdev->dev.coherent_dma_mask == DMA_MASK_NONE &&
-	    pdev->dev.dma_mask == NULL) {
-		pdev->dev.coherent_dma_mask = DMA_BIT_MASK(32);
-		pdev->dev.dma_mask = &pdev->dev.coherent_dma_mask;
-	}
-}