libav: update to 0.8.4

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
libav: move --enable-postproc to 0.8.4 recipe

libav 9.1 does not have this option.

Signed-off-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
libav: add support for AArch64

Signed-off-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>