tcl/target: Add config for XMOS XS1-XAU8A-10's ARM core

tcl/target: Add config for XMOS XS1-XAU8A-10's ARM core

The XS1-XAU8A-10 has 8 xCORE cores and one ARM core.
This config represents the ARM Cortex-M3 core, which is apparently
Silicon Labs EFM32 Giant Gecko IP.

Change-Id: I998360f096c759d2e274d96c1ca2e0450ba61146
Signed-off-by: Andreas Färber <afaerber@suse.de>
Reviewed-on: http://openocd.zylin.com/2762
Tested-by: jenkins
Reviewed-by: Oleksij Rempel
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-by: Paul Fertser <fercerpav@gmail.com>