gpu: ipu-v3: smfc: Convert to per-channel

Convert the smfc object to be specific to a single smfc channel.
Add ipu_smfc_{get|put} to retrieve and release a single smfc channel
for exclusive use, and add use counter to ipu_smfc_{enable|disable}.

Signed-off-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>