Fix compilation on ARM with android gcc 4.7

With the current code it fails due to running out
of registers.
So code the store offsets manually into the assembler
instead.
Passes "make fate-dts".

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
Add thread-safe wrapper for get_format().

Just like get_buffer, get_format should not be called from a different
thread if thread_safe_callbacks is not set.

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
Force dfa DAR to 4:3.

It seems very unlikely that the codec was ever meant to be used
on screens that have a different aspect ratio.
Fixes playback of LOGOS.DFA and 0002.dfa.