kernel: Add OpenOCD support

In order for OpenOCD to have a high-level view of an RTOS, it uses the
GDB protocol to obtain symbols from the system.

The GDB protocol, however, does not allow obtaining fields from
structures directly, and hardcoding offsets is not only brittle (due to
possibly different architectures or changes in the code), it's also
infeasible considering Zephyr is highly-configurable and parts of key
structs can be compiled in or out.

Export an array with offsets for these key structs. Also add a version
element in that array to allow changes in those structs.

Change-Id: I83bcfa0a7bd57d85582e5ec6efe70e1cceb1fc51
Signed-off-by: Leandro Pereira <leandro.pereira@intel.com>