configs: add defconfig for Nationalchip gx6605s dev board

gx6605s is a nice SOC for dvbs2 DVB product, and C-SKY inside.

Signed-off-by: Guo Ren <ren_guo@c-sky.com>
[Thomas: drop post-image script copying the gdbinit file, and suggest
to use gdb -x option instead to point to the gdbinit file in board/.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

board/csky/gx6605s/gdbinit

@@ -0,0 +1,25 @@
+tar jtag jtag://127.0.0.1:1025
+reset
+
+# setup CCR (Cache Config Reg)
+# 0-1:MP,2:IE,3:DE,4:WB,5:RS,6:Z,7:BE
+set $cr18 = 0x7d
+
+# vendor custom setup, double cache line & preload
+set $cr30 = 0xc
+
+# pin mux for serial8250
+set *(unsigned int *) 0xa030a14c |= (1 << 22) | (1 << 23)
+
+# pass devicetree blob
+# r2 is magic
+# r3 is address
+set $r2 = 0x20150401
+set $r3 = 0x92000000
+restore gx6605s.dtb binary 0x92000000
+
+# flush cache
+set $cr17 = 0x33
+
+load
+

board/csky/readme.txt

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+C-SKY Development Kit
+
+Intro
+=====
+
+C-SKY is a CPU Architecture from www.c-sky.com and has it own instruction set.
+Just like arm and mips in linux/arch, it named as 'csky'.
+
+gx6605s develop board is made by Hangzhou Nationalchip and C-SKY.
+
+Hardware Spec:
+  * CPU: ck610 up to 594Mhz
+  * Integrate with 64MB ddr2 in SOC.
+  * Integrate with hardware Jtag.
+  * Integrate with usb-to-serial chip.
+  * USB ehci controller in SOC.
+  * Power Supply: DC 5V from two micro-usb.
+
+How to build it
+===============
+
+Configure Buildroot
+-------------------
+
+The csky_gx6605s_defconfig configuration is a sample configuration with
+all that is required to bring the gx6605s Development Board:
+
+  $ make csky_gx6605s_defconfig
+
+Build everything
+----------------
+
+Note: you will need to have access to the network, since Buildroot will
+download the packages' sources.
+
+  $ make
+
+Result of the build
+-------------------
+
+After building, you should obtain this tree:
+
+    output/images/
+    ├── vmlinux
+    ├── rootfs.ext2
+    └── <board name>.dtb
+
+How to run it
+=============
+
+Prepare Jtag-Server
+-------------------
+
+  Download the Jtag-Server here:
+
+  https://github.com/c-sky/tools/raw/master/DebugServerConsole-linux-x86_64-V4.2.00-20161213.tar.gz
+
+  Go to the unpacked directory:
+
+  $./DebugServerConsole -ddc -rstwait 1000 -prereset -port 1025
+
+  Perhaps you need to use "sudo", which need libusb to detect c510:b210
+
+  $ sudo ./DebugServerConsole -ddc -rstwait 1000 -prereset -port 1025
+
+Prepare USB drive
+-----------------
+
+  You sould determine which device associated to the usb drive
+  carefully. eg:
+
+  $ cat /proc/partitions
+   8       48    1971712 sdd
+   8       49     976720 sdd1
+
+  $ sudo dd if=rootfs.ext2 of=/dev/sdd1
+  $ sudo sync
+
+Run
+---
+
+  Plug the usb drive on gx6605s dev board.
+
+  Setup the Console with the rate 115200/8-N-1.
+
+  $ ./output/host/usr/bin/csky-linux-gdb -x board/csky/gx6605s/gdbinit output/images/vmlinux
+