Add MIPS Ci20 jobs

Bug: skia:6423
NOTRY=true
Change-Id: I2193c49151359a174ffa071650e1dbd366c91b28
Reviewed-on: https://skia-review.googlesource.com/11783
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
5 files changed