wl18xx: export low/high band component values as module params

We use hardcoded values for the different board types.  In some cases
we may need to override the defaults, so export the values as module
params.  If not defined, the defaults for the specified board type
will be used.

Signed-off-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Arik Nemtsov <arik@wizery.com>