Describe the dynamic power coefficient of A57 and A53 CPUs.

Based on work by Gaku Inami <gaku.inami.xw@bp.renesas.com> and others.
Signed-off-by: NBiju Das <biju.das@bp.renesas.com>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>