iwlwifi: generalize d0i3_entry_timeout module parameter

The PCIe transport will also need a d0i3_entry_timeout_ms parameter,
so move the existing one from the slave transports to iwlwifi, so it
can be reused.  While at it, rename the parameter to something
shorter, namely d0i3_entry_delay.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>