MLK-20263: drm/imx/dcss: fix channel-0 line shift

If an RGB buffer is fed to channel-0, the output will have one line
shifted down, with the last line appearing on top.

Using the 7-tap filter will fix the issue. The 5-tap filter code will be
removed completely.

Signed-off-by: Dzung Hoang <dzung.hoang@nxp.com>
Signed-off-by: Laurentiu Palcu <laurentiu.palcu@nxp.com>