drm/omap: Use per-plane rotation property

The global mode_config.rotation_property is going away, switch over to
per-plane rotation_property.

Not sure I got the annoying crtc rotation_property handling right.
Might work, or migth not.

v2: Drop the BIT()
    Don't create rotation property twice for each primary plane

Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Rob Clark <robdclark@gmail.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
[danvet: Add comment per discussion between Tomi&Ville.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1474907460-10717-8-git-send-email-ville.syrjala@linux.intel.com