board: rockchip: Add LCKFB TaishanPi RK3566 Board

board: rockchip: Add LCKFB TaishanPi RK3566 Board

The LCKFB TaishanPi is a single-board computer based on the RK3566 SoC.

Specification:
- 1/2 Gib RAM
- Optinal EMMC
- SD-Card
- HDMI / MIPI CSI / MIPI DSI
- USB 2.0 Host (Type-A)
- USB 2.0 Host / OTG (Type-C)
- No Ethernet

This patch adds U-Boot support for the LCKFB TaishanPi RK3566 board, including:
- U-Boot device tree
- Default defconfig
- Board documentation
- MAINTAINERS entry

Changes in v2:
- Removed unused configs from `lckfb-tspi-rk3566_defconfig`
- Reordered TaishanPi entry in `doc/board/rockchip/rockchip.rst` alphabetically

Link to v1:
https://lore.kernel.org/u-boot/tencent_95ED0C0545D87B6A8C4B62EC045D53AD2406@qq.com/

Signed-off-by: Jiehui He <jiehui.he@foxmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>