iwlwifi: mvm/api: define system control command

The firmware is exposing a new system features control command,
define the necessary data structures etc. Rename "soc.h" to
"system.h" since the SoC command is also in the system group
and adding another file for just one more struct seemed like a
waste of files.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20211204174545.94a120687887.I79acffcf0793ea9e4ddec24b06420961bfb4fe94@changeid


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