PPC: [turbofan] Canonicalize return sequence for JSFunctions.

PPC: [turbofan] Canonicalize return sequence for JSFunctions.

Port 2b9112a578f66fc976557aededf3e203f48c395e

Original commit message:
This optimization is already implemented in fullcodegen, and
basically makes sure that we do not unecessarily blow up the
code with duplicated return sequences everywhere.

R=bmeurer@chromium.org, dstence@us.ibm.com, michael_dawson@ca.ibm.com
BUG=

Committed: https://crrev.com/3a1ef020cf8a5da2ec759a3bc630f3150d2490e4
Cr-Commit-Position: refs/heads/master@{#29333}

[MTBrandyberry, 2015-06-26 16:23:46]

mbrandy@us.ibm.com changed reviewers:
+ michael_dawson@ca.ibm.com
- michael_dawson@us.ibm.com

[donald.r.stence, 2015-06-26 16:34:48]

donald.r.stence@gmail.com changed reviewers:
+ donald.r.stence@gmail.com

[donald.r.stence, 2015-06-26 16:34:48]

lgtm

[MTBrandyberry, 2015-06-26 17:03:58]

The CQ bit was checked by mbrandy@us.ibm.com

[commit-bot: I haz the power, 2015-06-26 17:04:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1218493003/1

[commit-bot: I haz the power, 2015-06-26 17:04:13]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-06-26 17:04:13]

No L-G-T-M from a valid reviewer yet. Only full committers are accepted.
Even if an L-G-T-M may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[dstence, 2015-06-26 17:09:59]

lgtm

[MTBrandyberry, 2015-06-26 17:10:13]

The CQ bit was checked by mbrandy@us.ibm.com

[commit-bot: I haz the power, 2015-06-26 17:10:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1218493003/1

[commit-bot: I haz the power, 2015-06-26 19:48:38]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-26 19:48:59]

Patchset 1 (id:??) landed as
https://crrev.com/3a1ef020cf8a5da2ec759a3bc630f3150d2490e4
Cr-Commit-Position: refs/heads/master@{#29333}