drm/i915: Remove setparam ioctl

This was only used for the ums+gem combo, so ripe for removal now that
we only have kms code left.

v2: Drop fence_reg_start since it's now unused, noticed by Ville.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>