iwlwifi: initial contextification

In order to support multiple interfaces, we must move
a lot of data into per-context structures so we can
use the contexts the device offers. To start with,
this makes a lot of code context-aware, more changes
will move more things into the context structure.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>