iwlwifi: iwl-trans: move tfd to trans layer

The tfd_* code is not directly related to the PCIe transport,
so move the structures it uses to the common iwl-trans.h header.

Signed-off-by: Mordechay Goodstein <mordechay.goodstein@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20200924162105.a1a2ce2bce38.Ieada0fe087ebcc9bc84e22fc5abc9dba8914dd9f@changeid


Signed-off-by: Luca Coelho <luciano.coelho@intel.com>