Describe the dynamic power coefficient of A53 CPUs.

Based on work by Gaku Inami <gaku.inami.xw@bp.renesas.com> and others.
Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Link: https://lore.kernel.org/r/1568364608-46548-2-git-send-email-biju.das@bp.renesas.comSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>