drm/i915/gem: don't trust the dma_buf->size

At least for the time being, we need to limit our object sizes such that
the number of pages can fit within a 32b signed int. It looks like we
should also apply the same restriction to any imported dma-buf.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20210122181514.541436-1-matthew.auld@intel.com


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>