[turbofan] Load immortal heap objects from the heap roots.

It's cheaper to materialize heap constants by loading from the roots
array instead of embedding the constant into the instruction stream, at
least on x64, arm and arm64.

Drive-by-fix: Also cleanup the materialize constant from frame
optimization.

R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/1088913002

Cr-Commit-Position: refs/heads/master@{#27818}