mmal: Restore old buffer configuration

mmal: Restore old buffer configuration

With previours cleanups we reduced the number of allocated mmal buffers and
buffer headers. This caused some issues as the mmal components had to wait for
buffers frequently, which slowed them down. To avoid framedrops and even
picture stalls revert to the old buffer configuration, which wastes a bit
memory in theory but works way more reliably and smoothly.

Signed-off-by: Julian Scheel <julian@jusst.de>
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>