rockchip: ringneck_px30: migrate README to doc/board in rST format

This migrates the plaintext README in
board/theobroma-systems/ringneck_px30 to doc/board/theobroma-systems and
while doing so, update the instructions and rewrite it in rST.

Cc: Quentin Schulz <foss+uboot@0leil.net>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>

board/theobroma-systems/ringneck_px30/MAINTAINERS

@@ -4,6 +4,7 @@ M:	Klaus Goger <klaus.goger@theobroma-systems.com>
 S:	Maintained
 F:	board/theobroma-systems/ringneck_px30
 F:	board/theobroma-systems/common
+F:	doc/board/theobroma-systems/
 F:	include/configs/ringneck_px30.h
 F:	arch/arm/dts/px30-ringneck*
 F:	configs/ringneck-px30_defconfig

board/theobroma-systems/ringneck_px30/README

@@ -1,69 +1 @@
-Introduction
-============
-
-The PX30-uQ7 (Ringneck) SoM is a µQseven-compatible (40mmx70mm, MXM-230
-connector) system-on-module from Theobroma Systems[1], featuring the
-Rockchip PX30.
-
-It provides the following feature set:
-  * up to 4GB DDR4
-  * up to 128GB on-module eMMC (with 8-bit 1.8V interface)
-  * SD card (on a baseboard) via edge connector
-  * Fast Ethernet with on-module TI DP83825I PHY
-  * MIPI-DSI/LVDS
-  * MIPI-CSI
-  * USB
-    - 1x USB 2.0 dual-role
-    - 3x USB 2.0 host
-  * on-module companion controller (STM32 Cortex-M0 or ATtiny), implementing:
-    - low-power RTC functionality (ISL1208 emulation)
-    - fan controller (AMC6821 emulation)
-    - USB<->CAN bridge controller (STM32 only)
-  * on-module Espressif ESP32 for Bluetooth + 2.4GHz WiFi
-  * on-module NXP SE05x Secure Element
-
-Here is the step-by-step to boot to U-Boot on px30.
-
-Get the Source and build ATF binary
-===================================
-
-  > git clone https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git
-
-Compile the ATF
-===============
-
-  > cd trusted-firmware-a
-  > make CROSS_COMPILE=aarch64-linux-gnu- PLAT=px30 bl31
-  > cp build/px30/release/bl31/bl31.elf ../u-boot/bl31.elf
-
-Compile the U-Boot
-==================
-
-  > cd ../u-boot
-  > make CROSS_COMPILE=aarch64-linux-gnu- ringneck-px30_defconfig all
-
-Flash the image
-===============
-
-Copy u-boot-rockchip.bin to offset 32k for SD/eMMC.
-
-SD-Card
--------
-
-  > dd if=u-boot-rockchip.bin of=/dev/sdb seek=64
-
-eMMC
-----
-
-rkdeveloptool allows to flash the on-board eMMC via the USB OTG interface with
-help of the Rockchip loader binary.
-
-  > git clone https://github.com/rockchip-linux/rkdeveloptool
-  > cd rkdeveloptool
-  > autoreconf -i && ./configure && make
-  > git clone https://github.com/rockchip-linux/rkbin.git
-  > cd rkbin
-  > ./tools/boot_merger RKBOOT/PX30MINIALL.ini
-  > cd ..
-  > ./rkdeveloptool db rkbin/px30_loader_v1.16.131.bin
-  > ./rkdeveloptool wl 64 ../u-boot-rockchip.bin
+See doc/board/theobroma-systems/ringneck_px30.rst.