Add MB configs for remaining chromium.gpu builders
Add MB configs for remaining chromium.gpu builders

Add a placeholder config for the recipe_autogen bots, as well as adding
configs for the chromium.gpu and chromium.mac bots.

BUG=481692
R=dpranke

Review URL: https://codereview.chromium.org/1866923002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#386577}

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