Make the alignment parameter optional when negotiating buffers.
Default to a 16 bytes alignment and adjust for the max cpu
alignment.
Remove the useless align buffer parameter in plugins, we always
set it to 16 anyway.
This commit uses the video-src-alloc and video-play-reneg templates to create
examples for manual fixation at the format negotiation phase. These
clients simulate modifier negotiation done by clients handling DmaBufs.
Note: Neither client is capable of proper DmaBuf handling!
video-play-fixate can be used to test if a producer is capable to
fallback to shm buffer transport, while video-src-fixate can only be
used with the former example!
