Fix decoding of UTF-16 MMS

- In current implementation, Mms does not support
  UTF-8 as default charset
- Add change to use the charset that SMIL provides.
  If that is not present, decode by UTF-8. If there
  is an exception, then use ISO-8859-1 by default

CRs-Fixed: 648759
Change-Id: I48a059d01add68d672eb920ec4855fa065eb958e