flash_ec: openocd-related fix for npcx.cfg
flash_ec: openocd-related fix for npcx.cfg

using_jtag is now a helper function, not a global variable.

BUG=none
BRANCH=none
TEST=flash the npcx evaluation board

sudo servod --vendor 0x18d1 --product 0x5002
./util/flash_ec –port=9999 –board=npcx_evb

Change-Id: Ied2c0808b2a12d18b8350e68d5825703b71edc5e
Signed-off-by: Myles Watson <5fb4cec39c2b8f78857f7951c3db11d932932621@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/286531
Reviewed-by: Todd Broch <035f5b1f817cbb94019cec357b99778115602b63@chromium.org>

fourier49/BIZ_EC,fourier49/BIZ_EC,fourier49/BIZ_EC,fourier49/BIZ_EC