[turbofan] Allow encodable 64-bit constants as immediate for ARM64.

Also make sure that operands order for commutative 64-bit binary operations
are properly swapped when the constant is on the left hand-side.

R=bmeurer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/551543005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24114 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix profiler for TurboFan by reducing duplication.

R=titzer@chromium.org

Review URL: https://codereview.chromium.org/592703002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24115 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Adjust small heap threshold for idle time handler.

Follow-up for r23871.

BUG=chromium:407593
LOG=N
TBR=hpayer@chromium.org

Review URL: https://codereview.chromium.org/592053002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24116 ce2b1a6d-e550-0410-aec6-3dcde31c8c00