drm: Add a -puts() function for the seq_file printer

Add a puts() function to use seq_puts() to help speed up
up print time for constant strings.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>