drm/i915: Reorganize intel_rotation_info

Throw out a bunch of unnecessary stuff from struct intel_rotation_info,
and pull most of the remaining stuff to live under an array of
per-color plane sub-structures.

What still remains outside the sub-structure will be reorgranized later
as well, but that requires more work elsewhere so leave it be for now.

v2: Split the vma size == luma+chroma size fix to prep patch (Daniel)

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> (v1)
Link: http://patchwork.freedesktop.org/patch/msgid/1455569699-27905-8-git-send-email-ville.syrjala@linux.intel.com