Fix GKI exception of calling free on an already freed buffer

Fix GKI exception of calling free on an already freed buffer

Various parts of btif_hh.c were creating GKI buffers and
keeping references to them and freeing them in odd and
unnecessary ways.  The buffer is freed by lower levels
of the stack once the buffer has been sent to the chip
at the l2c layer and shouldn't be freed by btif_hh itself
since it's possible to double free, and there could
also be race conditions with other threads already processing
the buffer while the reference is freed if the API calls
are invoked again before the previous invocation was completely
processed.

Also added a helper routine to simplify buffer creation and
initialization.

Change-Id: Ia6039983502e2670b2325d90310244edf843b692
Signed-off-by: Mike J. Chen <mjchen@google.com>