drm: RIP mode_config->rotation_property

Now that all drivers have been converted over to the per-plane rotation
property, we can just nuke the global rotation property.

v2: Rebase due to BIT(),__builtin_ffs() & co.
    Deal with superfluous code shuffling

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
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/1477077768-4274-4-git-send-email-ville.syrjala@linux.intel.com