Port aom_reader_tell() support

This commit ports the following from aom/master:
4c46278 Add aom_reader_tell() support.
b9c9935 Remove an erroneous declaration.
56c9c3b Fix ANS build.

Change-Id: I59bd910f58c218c649a1de2a7b5fae0397e13cb1
7 files changed