tcl/board: add Linksys WAG200G config

tcl/board: add Linksys WAG200G config

The Linksys WAG200G router has a TI AR7 SoC and a 4MB Flash layout
similar to the Netgear DG834v3 router [1].

Below is an example of a successful flash recovery, using a TUMPA,
connected to the MIPS EJTAG 2.6 header (JP102) of the router.

     WAG200G [2]  TUMPA [3]
     Desc  Pin    Pin  Desc
    ------------------------
     nTRST   1    3   nTRST
     TDI     3    5     TDI
     TDO     5    13    TDO
     TMS     7    7     TMS
     TCK     9    9     TCK
     nSRST  11    15    RST
     GND     2    4     GND

Note that nSRST is optional to halt the CPU, but is required to probe
the flash. For instance, recover the kernel with:

    $ sudo ./src/openocd -s tcl \
      -f interface/ftdi/tumpa.cfg \
      -f tools/firmware-recovery.tcl \
      -c 'board linksys-wag200g;
          reset_config srst_only;
          flash_part kernel /path/to/kernel.bin;
          shutdown'

[1] https://wiki.openwrt.org/toh/linksys/wag200g
[2] https://www.linux-mips.org/wiki/JTAG#JTAG_headers
[3] http://www.tiaowiki.com/w/TIAO_USB_Multi_Protocol_Adapter_User's_Manual#20_PIN_JTAG_Connector

Change-Id: I952ba9f706e2e4f8f95ca03a5fa58f391ca030b6
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-on: http://openocd.zylin.com/3776
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>