iwlwifi: mvm: refactor SAR init to prepare for dynamic SAR

We are adding support for dynamic TX power tables for SAR (specific
absorption rate) compliance.  Currently, we only support a single
(static) TX power table, which is read from ACPI, and use it
statically.

To prepare for more tables that can be switched dynamically, refactor
the SAR init flow to allow reusage and add the current static table as
a single entry in an array of tables.

Signed-off-by: Haim Dreyfuss <haim.dreyfuss@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>