drm/i915: Refactor setting dma info to a common helper

DMA_MASK bit values are different for different generations.

This will become more difficult to manage over time with the open
coded usage of different versions of the device.

Fix by:
  disallow setting of dma mask in AGP path (< GEN(5) for i915,
  add dma_mask_size to the device info configuration,
  updating open code call sequence to the latest interface,
  refactoring into a common function for setting the dma segment
  and mask info

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
cc: Brian Welty <brian.welty@intel.com>
cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200417195107.68732-1-michael.j.ruhl@intel.com