intel: Generate multiple miplevels at once

Open Sagar Ghuge requested to merge sagarghuge/mesa:generate_multipl_mipmaps into main

This MR allow us to generate 2 LOD at once using subgroup operation. Time spend in blit operation is reduced by approx. 24% on Synmark's OglShMapPcf micro-benchmark on Gen12 platform.

Thanks to Ken, Matt and Jason for helping/mentoring me on this project!

Edited by Jordan Justen

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