boards: cc3220sf_launchxl: Enable standard flash/debug build targets

Previously, the cc3220sf platform could only be flashed using
TI UniFlash (or CCS) tools, requiring unique instructions.
Also, these procedures were not integrated with the standard Zephyr
build targets: 'flash', 'debug', 'debugserver'.

After installation of a TI OpenOCD v1.10 release, and other
one-time board setup, flashing and debugging can now be done
via OpenOCD/gdb, using the standard Zephyr build targets per
the Zephyr Application Development primer.

Signed-off-by: Gil Pitney <gil.pitney@linaro.org>