Refactor EmitUnOp to be templatized in the type and the emit function,
similar to EmitBinOp. This simplified adding f32 and f64 unops.

R=ahaas@chromium.org

Bug: v8:6600
Change-Id: Iaab473a3bbcc45673ff6190d6b56244c48bfa5a6
Reviewed-on: https://chromium-review.googlesource.com/937201
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51568}