doc: Bluetooth: Audio: Remake zephyr_gaf.svg to graphviz

Remake the Zephyr Generic audio framework (GAF) figure to a graphviz
version.
This makes it easier to modify it directly in the .rst file.

This also adds the missing GMAP/GMAS.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>