Allow flashing of EC binary from host with multiple servod invocations.
Allow flashing of EC binary from host with multiple servod invocations.

Adds argument --port to provide ability to flash from host that has
multiple servos running.

BRANCH=none
BUG=none
TEST=manual,

./util/flash_ec --board spring
- device connected to servod @ port 9999 is successfully flashed

./util/flash_ec --board spring --port 9902
- device connected to servod @ port 9902 is successfully flashed

Signed-off-by: Todd Broch <035f5b1f817cbb94019cec357b99778115602b63@chromium.org>
Change-Id: Iecc4b8df51236a1f21be5feca8bb87f5a1d03e97
Reviewed-on: https://gerrit.chromium.org/gerrit/43182
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

longsleep/ec,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BIZ_EC,eatbyte/chromium-ec,akappy7/ChromeOS_EC_LED_Diagnostics,akappy7/ChromeOS_EC_LED_Diagnostics,alterapraxisptyltd/chromium-ec,fourier49/BIZ_EC,mtk09422/chromiumos-platform-ec,coreboot/chrome-ec,eatbyte/chromium-ec,fourier49/BIZ_EC,thehobn/ec,gelraen/cros-ec,mtk09422/chromiumos-platform-ec,alterapraxisptyltd/chromium-ec,gelraen/cros-ec,eatbyte/chromium-ec,fourier49/BZ_DEV_EC,alterapraxisptyltd/chromium-ec,longsleep/ec,coreboot/chrome-ec,mtk09422/chromiumos-platform-ec,thehobn/ec,md5555/ec,coreboot/chrome-ec,thehobn/ec,fourier49/BZ_DEV_EC,coreboot/chrome-ec,gelraen/cros-ec,coreboot/chrome-ec,eatbyte/chromium-ec,coreboot/chrome-ec,alterapraxisptyltd/chromium-ec,fourier49/BZ_DEV_EC,fourier49/BIZ_EC,fourier49/BZ_DEV_EC,md5555/ec,md5555/ec,thehobn/ec,akappy7/ChromeOS_EC_LED_Diagnostics,longsleep/ec,akappy7/ChromeOS_EC_LED_Diagnostics,mtk09422/chromiumos-platform-ec,longsleep/ec,md5555/ec,gelraen/cros-ec