[autotest] Flash EC according to the chip name

The flash_ec doesn't keep all the board variants and doesn't know how
to program in some boards. Should call the flash_ec by passing the
chip name instead of the board name.

CQ-DEPEND=CL:287445,CL:287600
BUG=chromium:505003
TEST=Ran the following Python code to test:
> import common
> from autotest_lib.server.hosts import servo_host
> sh = servo_host.create_servo_host(DUT_IP_ADDRESS, {})
> sh._servo.program_ec(EC_IMAGE_PATH)

Change-Id: I82e9e2cc5c4ab6fd4d7eef0a977f665bc8b4f842
Reviewed-on: https://chromium-review.googlesource.com/287601
Trybot-Ready: Wai-Hong Tam <waihong@chromium.org>
Tested-by: Wai-Hong Tam <waihong@chromium.org>
Reviewed-by: Dan Shi <dshi@chromium.org>
Commit-Queue: Wai-Hong Tam <waihong@chromium.org>
2 files changed