arm64: dts: allwinner: a64: add simplefb for A64 SoC

The A64 SoC features two display pipelines, one has a LCD output, the
other has a HDMI output.

Add support for simplefb for the LCD output. Tested on Teres I.

This patch was inspired by work of Icenowy Zheng.

Signed-off-by: Harald Geyer <harald@ccbib.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>