diag: Enable APSS diag hdlc encoding

Currently, the hdlc encoding of data is performed on the peripherals.
Enable APSS diag hdlc encoding so that the data will be encoded on
the apps for the peripherals that support this feature.

Change-Id: Ie5c8f39b59c544c9b91c3693c32a90560c0ae329
Signed-off-by: Dixon Peterson <dixonp@codeaurora.org>