configs/orangepi_pc2: new defconfig

This patch adds a new defconfig for OrangePI PC2 board.

It was supported before in Buildroot, however due to problems in
building TF-A, it was removed in commit
eeede611f8. This commit re-adds it, in a
state that properly builds.

Signed-off-by: Javad Rahimi <javad321javad@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

board/orangepi/orangepi-pc2/readme.txt

@@ -0,0 +1,37 @@
+Intro
+=====
+
+This default configuration will allow you to start experimenting with the
+buildroot environment for the Orangepi PC2. With the current configuration
+it will bring-up the board, and allow access through the serial console.
+
+Orangepi PC2 link:
+http://www.orangepi.org/html/hardWare/computerAndMicrocontrollers/details/Orange-Pi-PC-2.html
+
+Sunxi Wiki link:
+https://linux-sunxi.org/Xunlong_Orange_Pi_PC_2
+
+This configuration uses U-Boot mainline and kernel mainline.
+
+How to build
+============
+
+    $ make orangepi_pc2_defconfig
+    $ make
+
+Note: you will need access to the internet to download the required
+sources.
+
+How to write the SD card
+========================
+
+Once the build process is finished you will have an image called "sdcard.img"
+in the output/images/ directory.
+
+Copy the bootable "sdcard.img" onto an SD card with "dd":
+
+  $ sudo dd if=output/images/sdcard.img of=/dev/sdX
+  $ sudo sync
+
+Insert the micro SDcard in your Orangepi PC2 and power it up. The console
+is on the serial line, 115200 8N1.