flash_ec: Add a chip argument
flash_ec: Add a chip argument

The flash_ec uses the given board name to select a proper flashing
method. It keeps a mapping from board name to chip name.
This approach is not scalable if we want this script to work on
all supported board variants, like the pinky family which has many
boards: jerry, minnie, speedy, etc.

This change adds a new argument of chip name, such that we can only
keep the mapping of major boards. Other boards not listed can use
the chip argument to select a proper flashing method.

BRANCH=none
BUG=chromium:505003
TEST=Ran the script on Beaglebone/Servo v3 connected with Jerry:
$ flash_ec --chip stm32 --image ec.bin

Change-Id: I553ee68f82a7985a37548dfb6e89b364eaffd0f1
Signed-off-by: Tom Wai-Hong Tam <04b587fdf5845741a0c5a8b9cd59ca72d73ef8fc@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/287445
Reviewed-by: Dan Shi <ddf10325a07dcd5610d94b7b9f19da3abc09e645@chromium.org>
Reviewed-by: Myles Watson <5fb4cec39c2b8f78857f7951c3db11d932932621@chromium.org>

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