va: vpp: refactor static props and add scale-method
Added scale-method setter to vafilter so that it can be used in vapostproc and vacompositor.
Added scale-method property to vapostproc element.
Moved static/unconditional prop install from vafilter to vapostproc.
Resolves #1250 (closed)
cc: @vjaquez @He_Junyan
Edited by U. Artie Eoff