seabios: upgraded package to upstream

Upgraded sys-firmware/seabios to version 1.7.3.

BUG=chromium:220911
TEST=`cbuildbot {arm,amd64,x86}-generic-full` passes

Change-Id: I0b5eac6a2d85cce328a1496a9068daa67fc4f7aa
Reviewed-on: https://chromium-review.googlesource.com/196112
Reviewed-by: Gaurav Shah <gauravsh@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
4 files changed