PPC: Debugger: prepare code for debugging on a per-function basis.

PPC: Debugger: prepare code for debugging on a per-function basis.

Port 35c28ce0a742e58346d2dea009428cacd442040d

Original commit message:
    Prior to this patch, we enter a global debug mode whenever a break point
    is set. By entering this mode, all code is deoptimized and activated
    frames are recompiled and redirected to newly compiled debug code.

    After this patch, we only deoptimize/redirect for functions we want to
    debug. Trigger for this is Debug::EnsureDebugInfo, and having DebugInfo
    object attached to the SFI prevents optimization/inlining.

    The result is that we can have optimized code for functions without break
    points alongside functions that do have break points, which are not
    optimized.

R=yangguo@chromium.org, dstence@us.ibm.com, michael_dawson@ca.ibm.com
BUG=v8:4132
LOG=N

Review URL: https://codereview.chromium.org/1244823002

Cr-Commit-Position: refs/heads/master@{#29764}