mm-video-legacy: vdec: add YUV420SP output format support

Add YUV420SP support and advertize this ahead of YUV420P.
Clients which need linear YUVs for editing can use this format
rather than YUV420P.
TILE -> 420SP conversion fairs better in performance and quality
as compared to 420P

Bug: 17188136
Change-Id: I4085d2e9c268e839d78f9bf4ff444de68278d272