media: minor fixes for MediaCodecInfo

- use equals() for Range singularity checks
- parse max-channel-count properly
- add platform defaults to G711 and GSM audio codecs
- allow xml to override platform limits if format,
  profile or level is not supported (but recognized to be
  possibly valid) by the platform
- set defaut format fields

Bug: 11990470
Change-Id: I06114e2d10dcc205a8a963605a01e6d4f6ecd0f0