cros_workon_make: move here

To help consolidate, move this script out of platform/dev/host/.
We're largely turning down that directory, and this script is
better here with the other remaining build shell scripts.

BUG=None
TEST=None

Change-Id: I734ef610e508a1f8ca3e1e362ae631d832b6902e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2574666
Reviewed-by: Alex Klein <saklein@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Nicolas Boichat <drinkcat@chromium.org>