python 3.8: Update SDK dependency ebuilds PYTHON_COMPAT to include 3.8

For enabling Python 3.8 in the SDK, packages in the
virtual/target-chromium-os-sdk dependency tree need to include Python
3.8 in the PYTHON_COMPAT field.

BUG=b:187794810
TEST=pass CQ

Change-Id: Id21eda64f60d697ac22ae82acb0149b272129854
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/3894752
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Sloan Johnson <sloanjohnson@google.com>
Tested-by: Sloan Johnson <sloanjohnson@google.com>
70 files changed