iwlwifi: trans: configure the scheduler enable register

Currently the firmware is handling this, but that is wrong as it then
needs to assume a certain command queue, therefore this should be in
the driver; add it here so it can be removed from the firmware in the
future.

Signed-off-by: Avri Altman <avri.altman@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>