drm/armada: pass plane state into armada_drm_plane_calc_addrs()

armada_drm_plane_calc_addrs() gets all its information from the plane
state, so it makes sense to pass the plane state pointer down into this
function, rather than extracting the information in identical ways,
sometimes a couple of layers up.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>