drm/i915: Treat stolen memory as DMA addresses

The conversion of stolen to use phys_addr_t (from essentially u32)
sparked an interesting discussion. We treat stolen memory as only
accessible from the GPU (the DMA device) - an attempt to use it from the
CPU will generate a MCE on gen6 onwards, although it is in theory a
physical address that can be dereferenced from the CPU as demonstrated
by earlier generations. As such, using phys_addr_t has the wrong
connotations and as we pass the address into the DMA device via
dma_addr_t (through the scatterlists used to program the GTT entries),
we should treat it as dma_addr_t throughout.

Signed-off-by: Chris Wilson <[email protected]>
Cc: Paulo Zanoni <[email protected]>
Cc: Ville Syrjälä <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]
Reviewed-by: Paulo Zanoni <[email protected]>

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