iwlagn: introduce transport layer and implement rx_init

The transport layer is responsible for all the queues, DMA rings etc...
This is the beginning of the separation of all the code that is tighly
related to HW design to the aforementioned transport layer.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>