va: vpp: Fix features lost in transform_caps().

va: vpp: Fix features lost in transform_caps().

When we transform the caps from the sink to src, or vice versa, the
"caps" passed to us may only contain parts of the features. Which
makes our vpp lose some feature in caps and get a negotiation error.
The correct way should be:
Cleaning the format and resolution of that caps, but adding all VA,
DMA features to it, making it a full feature caps. Then, clipping it
with the pad template.

fixes: #1551

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2081>