Avoid R8 EGLImages on Mali GPUs with Android <= 9

R8 EGLImage siblings cannot be rendered to or have data uploaded
to them on some Mali devices. The validating command decoder works
around this limitation by directly sharing the source texture for
the EGLImage but the passthrough command decoder cannot because full
cross-context and cross-thread usage of the EGLImages is needed for
DrDC.

Instead, fall back to L8 textures for video decoding. The video
pipeline will still be entirely on the GPU but drivers may need to do
internal workarounds and emulation to support luminance textures.

Bug: chromium:1455752
Bug: chromium:1117370
Change-Id: Iec291e790062d686314959cafc5273c52599d98e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4784967


Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1184844}