Change TOSA specification to signless types

Integer inputs and outputs to TOSA operators are now defined as signless
values. In most instances the operator will used signed arithmetic as
indicated in previous versions of the specification resulting in little
functional change to the specification.

New attributes have been added to the RESCALE operator to indicate
whether the input and output values should be treated as signed or unsigned.

Explicit use of static_cast, sign_extend, zero_extend and truncate are added
to the pseudocode to avoid ambiguity.

Change-Id: I71c67d3e5aeaabc418c768f821fce6ee3eebb65b