drm: Add support for optional per-plane rotation property

Not all planes on the system may support the same rotations/reflections,
so make it possible to create a separate property for each plane.
This way userspace gets told exactly which rotations/reflections are
possible for each plane.

v2: Add drm_plane_create_rotation_property() helper
v3: Drop the BIT(), __builtin_ffs(x) - 1,
    Moar WARNs for bad parameters
    Deal with superfluous code shuffling

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> (v1)
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1474907460-10717-4-git-send-email-ville.syrjala@linux.intel.com