vaapivideomemory: refactor code for readability
vaapivideomemory: refactor code for readability

Added the inlined function allocator_configure_pools() moving out code
from gst_vaapi_video_allocator_new() to make clear that it is a
post-initalization of the object.

GStreamer/gstreamer-vaapi,GStreamer/gstreamer-vaapi,ceyusa/gstreamer-vaapi,ceyusa/gstreamer-vaapi