wl1271: Update handling of the NVS file / INI parameters

This patch updates the handling of the NVS file INI-section, trying to make
it slightly more generic, and exposing the parameters being set. This is done
in preparation for 5GHz parameters.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>