vdec: add and use configure_caps()
vdec: add and use configure_caps()

The configuration of the output caps (source pad) is getting
complex and it may get worse. So it is a good idea use a
function for it.

No functional changes.

Signed-off-by: Víctor Manuel Jáquez Leal <853e0dbb5ddd43a0f0483f24794ae05c4c52af91@igalia.com>

community-ssu/gst-dsp,felipec/gst-dsp,felipec/gst-dsp,community-ssu/gst-dsp,community-ssu/gst-dsp