drm/i915: Use an array of register tables in command parser

For Haswell, we will want another table of registers while retaining
the large common table of whitelisted registers shared by all gen7
devices.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
[danvet: Pipe patch through sed -e 's/\<ring\>/engine/g' to make it
apply.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>