arm64: dts: mt8173: Add capacity-dmips-mhz attributes

Dhrystone benchmark on Acer Chromebook R13 CB5-312T:
A72: 15698587 dps @ 1807 MHz
A53:  7598784 dps @ 1703 MHz

Signed-off-by: Ulrich Hecht <uli-qwV78thtvt0@public.gmane.org>
Link: https://lore.kernel.org/r/1563529816-3992-1-git-send-email-uli@fpond.eu


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>