AArch64: Improve codegen of AdvSIMD logf function family

AArch64: Improve codegen of AdvSIMD logf function family

Load the polynomial evaluation coefficients into 2 vectors and use lanewise MLAs.
8% improvement in throughput microbenchmark on Neoverse V1 for log2 and log,
and 2% for log10.

Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>
(cherry picked from commit d6e034f5b222a9ed1aeb5de0c0c7d0dda8b63da3)