[imageburner] refactor makefile

Refactor the Makefile to reduce dummy variable use, generally clean it up. Also,
use libchromeos.pc instead of hardcoding library dependencies.

BUG=chromium-os:24959
TEST=build

Change-Id: I57c612f2b4903f1e63795dad2af7b3603238bc0c
Signed-off-by: Elly Jones <ellyjones@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/14404
Reviewed-by: Mike Frysinger <vapier@chromium.org>
2 files changed