Deprecate PmLogPrint APIs and direct to "legacy-log" context

- Direct messages from the old APIs to a context and file called
  "legacy-log". This context can later be redirected to /dev/null.
- Update doxygen to reflect code sample for new API usage.

[GF-5675] PmLogPrint and PmLogVPrint APIs to be marked for deprecation
[GF-5681] Redirect output from PmLogPrint and PmLogVPrint APIs to a
          different context

Open-webOS-DCO-1.0-Signed-off-by: Gayathri Srinivasan <gayathri.srinivasan@lge.com>

Change-Id: I0dabac9f7bce6b5caf6f11b07db1683f7ece91f0