Draft: anv/blorp: Make use of MRT for clears to reduce invalidates & stalls
This MR tries to implement the suggestion in #10872 and allows the blorp shader to support multiple render targets as well as updating LOAD_OP_CLEAR in anv to make use of multiple render target.
This MR still needs work to make sure the multiclear path is taken in all cases where it would work, but I'm creating a draft MR right now to get feedback on the approach to make sure I'm understanding the original suggestion properly.