[ARM64] [turbofan] Support uxtb/uxth for add/sub.

[ARM64] [turbofan] Support uxtb/uxth for add/sub.

Add support for appending extend modes uxtb or uxth to add and subtract
instructions, and using them in the instruction selector.

BUG=

Committed: https://crrev.com/3fdfe613f8e099854453c994f073b64d8ad97bc2
Cr-Commit-Position: refs/heads/master@{#27303}

[jbramley, 2015-03-18 15:21:28]

jacob.bramley@arm.com changed reviewers:
+ bmeurer@chromium.org, ulan@chromium.org

[jbramley, 2015-03-18 15:51:04]

On 2015/03/18 15:21:29, jbramley wrote:

Oops, sorry. I'll look into the test failures.

[jbramley, 2015-03-18 16:52:38]

On 2015/03/18 15:51:04, jbramley wrote:
> On 2015/03/18 15:21:29, jbramley wrote:
> 
> Oops, sorry. I'll look into the test failures.

Fixed, sorry for the noise.

[Benedikt Meurer, 2015-03-19 05:00:51]

Nice. LGTM

[jbramley, 2015-03-19 10:15:51]

The CQ bit was checked by jacob.bramley@arm.com

[commit-bot: I haz the power, 2015-03-19 10:15:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1021533002/20001

[commit-bot: I haz the power, 2015-03-19 12:44:13]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-03-19 12:44:29]

Patchset 2 (id:??) landed as
https://crrev.com/3fdfe613f8e099854453c994f073b64d8ad97bc2
Cr-Commit-Position: refs/heads/master@{#27303}