iwlwifi: enable custom fw regulatory solution

This enables the custom firmware regulatory solution option
on iwlwifi drivers. These devices are uncapable of mapping their
EEPROM regulatory domain to a specific ISO / IEC alpha2.
Although the new 11n devices (>= iwl 5000) have only
3 regultaory SKUs -- MOW, ABG (no N) and BG -- the older
devices (3945 and 4965) have a more complex SKU arrangement
and therefore its not practical to move this to the driver.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Acked-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>