axfer: open file descriptor outside of container module

axfer: open file descriptor outside of container module

Internal container module operates file descriptor to media file. For
this purpose, the structure has fd member and any file operation is done
internally. However, the case to use special file descriptor such as
memfd requires to maintain file descriptor externally.

This commit opens file descriptor outside of container module. The
internal APIs to initialize container get an argument for the file
descriptor instead of file path.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>