iwl-trans: move dev_cmd_offs, page_offs to a common trans header

dev_cmd_offs, page_offs field 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.20200926002540.83b41765961f.Icd12bfb2a736ccf4cbe080973c746fb70a3c4a50@changeid


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