libstagefright: Use 3gp4 ftyp box when AMR audio is present

mp42 boxes do not support the 'damr' box type whereas 3gp4 boxes
explicitly support it. Using mp42 makes clips with AMR incompliant
with mpeg4 standards and unplayable by many media players. To
ensure interoperability, use a 3gp4 box if the recorded clip
contains AMR audio.

CRs-Fixed: 721883
Change-Id: I75e3558cd5088d05d36104abfb04a3c0c1d1a4e7