pan/bi: Lower fsqrt

For G72+ anyway. G71 will want something a bit more fine grained. I hope
this has enough precision for GL (the blob apparently does some exponent
fixup).

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <mesa/mesa!4530>
27 jobs for !4530 with bifrost-2 in 10 minutes and 33 seconds (queued for 4 seconds)
merge request