cros_update_firmware: Split srcuris across lines.

- Should allow easier merging of these files in git.
- Also edit cros_unibuild_config.py to do this.

BUG=b:170505117, b:172060960
TEST=CQ
TEST=cros_update_firmware -b dedede -p drawcia
TEST=cros_update_firmware -b dedede

Change-Id: I2fa04062cd5cfc53044904778cc78a3a559ce509
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2495563
Reviewed-by: YH Lin <yueherngl@chromium.org>
Reviewed-by: Jack Rosenthal <jrosenth@chromium.org>
Tested-by: Andrew Lamb <andrewlamb@chromium.org>
Commit-Queue: Andrew Lamb <andrewlamb@chromium.org>
(cherry picked from commit bc1c80ab8d158d78d53f92dea991e082a76a1a1e)
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2550851
Tested-by: Chen-Tsung Hsieh <chentsung@chromium.org>
Reviewed-by: Chen-Tsung Hsieh <chentsung@chromium.org>
Commit-Queue: Chen-Tsung Hsieh <chentsung@chromium.org>