…n adreno r=kvark

Previously we were using 256 bytes (which happens to be equal to 64
pixels for RGBA8 textures). A recent change to the GPU Cache uncovered
the fact that the requirement is actually 64 pixels, eg 1024 bytes for
RGBAF32 textures.

Differential Revision: https://phabricator.services.mozilla.com/D70915

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/f5be65b0b22b10f878d6eb297adb68eb3ab82e39