drm/format-helper: Unify the parameters of all per-line conversion helpers

Give each per-line conversion helper pointers of type void and the
number of pixels in the line. Remove the unused swab parameters.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220427141409.22842-4-tzimmermann@suse.de