rtos: Add ChibiOS/RT support

rtos: Add ChibiOS/RT support

This patch adds ChibiOS/RT support. This patch requires at least
ChibiOS/RT development version starting from SVN revision 4734.

Note, that the Thread structures depend not only on the target
but also on the ChibiOS configuration at build time.
To correct this ChibiOS includes a new "memory signature" which
specifies the offsets.

Special thanks go to Peter Stuge and Spencer Oliver for their
continous input and feedback to this patch.

Change-Id: I842bf7ba6c2309a4efe93d29ea6cd0784a8b22a3
Signed-off-by: Matthias Blaicher <matthias@blaicher.com>
Reviewed-on: http://openocd.zylin.com/901
Tested-by: jenkins
Reviewed-by: Peter Stuge <peter@stuge.se>