rtos: Use ARRAY_SIZE instead of coding it by hand

rtos: Use ARRAY_SIZE instead of coding it by hand

Use ARRAY_SIZE in helper/types.h to determine the size of the
symbol list.

Change-Id: Icc9838323510f8602efa5d0162a4daed33f863b9
Signed-off-by: Matthias Blaicher <matthias@blaicher.com>
Reviewed-on: http://openocd.zylin.com/935
Tested-by: jenkins
Reviewed-by: Peter Stuge <peter@stuge.se>