diag: Fix concurrency issues when processing userspace inputs

Diag does not properly accomodate multiple clients when processing
certain types of userspace inputs. With multiple clients running this
will lead to concurrency issues.  Make modifications to use a memory
pool to support multiple clients.

Also, there is a memory leak issue related to dci initialization and
exit. In addition, requested logging modes are not being validated.
Make modifications to the code to correct these issues.

Change-Id: Ieda46434b58683184ae4e16ccd1c609f21ab7962
Signed-off-by: Dixon Peterson <dixonp@codeaurora.org>