Q formats should not be used as storage types

[christophe0606]

If I look at arm_dot_prod_q15, the comment of the function is:

The return result is in 34.30 format

and the return type is q63_t

So q63_t is here used as a storage type. The real fixed type being q34_30_t

The same problems is present in every function where the datatype are not q63, q15 or q7 but other fixed point types are used.

This should be improved.