iteflash: exit DBGR mode after flashing
iteflash: exit DBGR mode after flashing

This change is separated from CL:344481.

We need a cold reset after flashing, but we kill 'servod' before
execute iteflash for each flashing process.

With this change, we can restart 'servod' again without errors.
And we are able to use dut-control to do a EC cold reset.

BRANCH=none
BUG=none
TEST=flashing completed, and wait for servo's cold reset.

Change-Id: Ifc242467211253fabcd733a971e999baa68a1026
Signed-off-by: Dino Li <338d523ecf3700bd86eb9c34d220f91911d2a18c@ite.com.tw>
Reviewed-on: https://chromium-review.googlesource.com/488002
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec