board: rockchip: Add Pine64 PineTab2

The Pine64 PineTab2 is a tablet computer based on the Rockchip RK3566
SoC. The table features 4/8 GB LPDDR4 RAM and 64/128 GB eMMC storage.

Features tested on a Pine64 PineTab2 8GB v2.0:
- SD-card boot
- eMMC boot
- SPI Flash boot
- USB host

Device tree is imported from linux maintainer branch v6.9-armsoc/dts64,
commit 1b7e19448f8f ("arm64: dts: rockchip: Add devicetree for Pine64
PineTab2").

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>