anv: Support fast clears in anv_CmdClearColorImage
What does this MR do and why?
anv: Support fast clears in anv_CmdClearColorImage
At least two game traces make use of this path: TWWH3 and Factorio.
This was split off from a branch I'm working on which enables fast clears more often (part of #11418). The performance CI reports no significant changes.
/cc @fjdegroo