media: rp1: cfe: Improve link validation for metadata

Improve the link validation for metadata by:
- Allowing capture buffers that are larger than the incoming frame
  (instead of requiring exact match).

- Instead of assuming that a metadata unit ("pixel") is 8 bits, use
  find_format_by_code() to get the format and use the bit depth from
  there. E.g. bit depth for RAW10 metadata will be 10 bits, when we
  move to the upstream metadata formats.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>