d2-common: enable background scan

and TDLS mode, should do nothing on d2, but useful for the prima targets

Change-Id: I3225473f64b03310bce5a3fee0ea775da9aed8ae
d2-common: fix up modem links

Ensure /firmware is mounted before generating the links

Change-Id: I14f5c1c4418aa6756eea2cd77cb7ab6bcd986d4a