For the history, the parallel disable port has been introduced by:
"00be69f4 omxvideodec: Disable output port when setting a new format"
and then replicated to videoenc, audiodec and audioenc.

This is only required to do 'parallel' if buffers are shared between ports.
But for decoders and encoders the input and output buffer are of different
nature by definition (bitstream vs images). So they cannot be shared.

Also starting from IL 1.2.0 it is written in the spec that the parallel
disable is not allowed and will return an error. Except when buffers are
shared.

Again here we know in advance that they are not shared so let's always
do a sequential disable.

Tested on Desktop, rpi and zynqultrascaleplus.

https://bugzilla.gnome.org/show_bug.cgi?id=786348