Replace min-num-framebuffers property with num-additional-framebuffers

This makes more sense, since usually, one wants to specify additional
framebuffers instead of an absolute number

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>
Log level cleanup + extra comments

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>
Add grayscale format to list of motion JPEG pixel formats

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>