Use servo to boot EC into the flashing mode. Use the unified control
ec_boot_mode to do so.
CQ-DEPEND=CL:1018206
BRANCH=none
BUG=b:68707064
TEST=Ran the flash_ec script on Cheza using servo-micro
TEST=Ran the flash_ec script on Meowth using CCD, with some servo
overlays to drive the ccd_ec_boot_mode control
Change-Id: I32dfe5baa82dd842b5237f38ea971c09e91c47d3
Signed-off-by: Wai-Hong Tam <waihong@google.com>
Reviewed-on: https://chromium-review.googlesource.com/1020159
Reviewed-by: Alexandru M Stan <amstan@chromium.org>