PPC: Debugger: use debug break slot to break on call.

PPC: Debugger: use debug break slot to break on call.

Port 8965b683ce39bc3c24ed2466d189323d81a70852

Original commit message:
    Break point at calls are currently set via IC. To change this, we
    need to set debug break slots instead. We also need to distinguish
    those debug break slots as calls to support step-in.

    To implement this, we add a data field to debug break reloc info to
    indicate non-call debug breaks or in case of call debug breaks, the
    number of arguments. We can later use this to find the callee on the
    evaluation stack in Debug::PrepareStep.

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

Committed: https://crrev.com/16e5c248958fc2e68eae4dae33146331aca827d8
Cr-Commit-Position: refs/heads/master@{#29582}

[dstence, 2015-07-10 20:37:05]

lgtm

[MTBrandyberry, 2015-07-10 20:37:40]

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

[commit-bot: I haz the power, 2015-07-10 20:37:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1231173002/1

[commit-bot: I haz the power, 2015-07-10 21:02:26]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-10 21:02:46]

Patchset 1 (id:??) landed as
https://crrev.com/16e5c248958fc2e68eae4dae33146331aca827d8
Cr-Commit-Position: refs/heads/master@{#29582}