iwlwifi: make EEPROM enhanced TX power a bool

There's no need to carry around the function
pointer when a boolean indicating that the
EEPROM stores enhanced TX power information
is sufficient.

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