It is possible for there to be multiple encryption init info structure.
For example, to support multiple key systems or in key rotation.  This
changes the AVEncryptionInitInfo struct to be a linked list so there
can be multiple structs without breaking ABI.
Signed-off-by: Jacob Trimble <modmaker@google.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>