vivado: improve timing during opt_design

[occheung]

Summary

Specify the ExploreWithRemap directive while optimizing the logic design in vivado. Below is the description of the related directives in vivado 2021.1 (UG835):

ExploreArea - Run multiple passes of optimization, with an emphasis on reducing area.
ExploreWithRemap - Similar to ExploreArea but adds the remap optimization to compress logic levels.
AddRemap - Run the default optimization, and include LUT remapping to reduce logic levels.