Add gray_8_as_lum and _as_red private grpixelconfigs

Bug: skia:
Change-Id: I70cbd0bc9f7a7a16fb9f0688d272d7afa607700a
Reviewed-on: https://skia-review.googlesource.com/80622
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
12 files changed