arc: Add linker command file for Harvard architecture

Some ARC CPUs can be built with separate instruction bus
and data bus (i.e. Harvard Architecture). Such systems
have only ICCM and DCCM memories. When CONFIG_HARVARD
is defined, the initial stack pointer is set to the
TOP of the DCCM memory. Currently there is no SOC that
existing in Zephyr tree that sets CONFIG_HARVARD, but
this will be coming soon.

Change-Id: I2016d1f472fbdad683a964aa0b65c5263ecfb6cf
Signed-off-by: Chuck Jordan <cjordan@synopsys.com>