plugin: if any caps in downstream, negotiate raw video

When downstream has any caps, vaapi should not shovel vaapi featured
buffers, but rather plain raw video, assuming always the worst case
scenario (downstream cannot handle featured video memory but raw
system memory buffers).

This patch query the peer caps without any filter, to know if
donwstream just ask for any caps, if so jump to the color space
checking, otherwise do the caps intersection and continue with the
feature selection algorithm.

Fixes: #139
8 jobs for any-caps in 21 minutes and 9 seconds (queued for 9 seconds)
Status Job ID Name Coverage
  Preparation
passed #143246
gst indent

00:00:21

passed #143245
manifest

00:00:32

 
  Build
passed #143247
build fedora x86_64

00:06:48

 
  Test
passed #143248
check fedora

00:03:14

 
  Full Builds
passed #143249
build android arm64 api28

00:03:28

passed #143251
build cerbero cross win32

00:07:03

passed #143252
build cerbero cross win64

00:07:29

passed #143250
build cerbero fedora x86_64

00:07:21