arm64: dts: renesas: r8a774a1: Add dynamic power coefficient

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: Biju Das <biju.das@bp.renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>