Board support for the ARC EM Starter Kit provides for a board
that can select one of two SOCs. The EM9D and EM11D commits
will be done separately to expidite review. Also submitted here
is doc/board/em_starterkit.rst to explain details about this
Zephyr board choice.
Change-Id: Icd9fac045c700ad8dcb95161fdd63c130f665778
Signed-off-by: Chuck Jordan <cjordan@synopsys.com>