Add a board file for the Glyn Tonga2.

Add a board file for the Glyn Tonga2.

This is a Toshiba TMPA900CMXBG (ARM9) based SO-DIMM CPU module with 64MB
DDR SDRAM, 256MB NAND flash, and on-board Ethernet.

The board file provides a tonga2_init function which sets up the
PLL/clocks and memory (SDRAM and SRAM), which allows writing a boot-loader
into RAM via JTAG.

Change-Id: I60522b97997bdf50e1f25aebab910d93a98522fb
Signed-off-by: Uwe Hermann <uwe@hermann-uwe.de>
Reviewed-on: http://openocd.zylin.com/19
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>
Tested-by: Spencer Oliver <spen@spen-soft.co.uk>