Port 9b3174b2

Original Commit Message:

    Remove all IsHeapObject/IsSmi checks from assembler and also from
    the macro-assembler functions that Turbofan code generation uses.

    Note for porters: In case it's unclear which macro-assembler
    functions need to be modified, it may be best to wait until I
    split MacroAssembler in a followup-CL, which will make that clear.

R=neis@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=v8:6048
LOG=N

Change-Id: Iae7d74709930a25246ab919a65dfecf1175945f7
Reviewed-on: https://chromium-review.googlesource.com/562656Reviewed-by: Junliang Yan <jyan@ca.ibm.com>
Commit-Queue: Jaideep Bajwa <bjaideep@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#46458}