Add a tuple type for packing

At the top level, payload had the ability to pack a tuple, but it did it
by splitting it into its parts and packing those individually. But if
one of those parts was a tuple, it would fail. This moves the tuple
packing code into the packing templates so that it is possible to pack a
nested tuple of tuples.

Tested-by: newly written tuple unit tests pass

Change-Id: Icd80926314072df78b0083a823dcfb46e944e365
Signed-off-by: Vernon Mauery <vernon.mauery@linux.intel.com>
3 files changed