ti_wpan: build wpan only if device requires it

to enable set BOARD_WPAN_DEVICE := true
ti-wpan: Enable FM app flag check

Enable the FM flag check since some devices using TI wl12xx chips don't have working FM radio

Signed-off-by: Michael Bestas <mikeioannina@gmail.com>

Change-Id: I3153371811dfa4b7da5404ee7cd04607e69b3a2e