board_beetle: Add support for ARM V2M Beetle Board

Add board support for ARM V2M Beetle platform.

ARM V2M Beetle board is build around the ARM Beetle Cortex-M3
based processor.

The support has been tested in nanokernel mode with the bringup
application that will be pushed with a future patch.

Jira: ZEP-1245
Change-Id: Ib05a40c072f10149e692283177387cf2cfe32f66
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@linaro.org>
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>