DPMS functionality is only used by the CRTC's enable and disable
functions. Inline the code. The patch also adds symbolic constants
for the blank register and constants; according to udlfb, which is
a bit more detailed than DRM's udl.

v3:
	* use symbolic constants for blank, according to udlfb driver
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191210084905.5570-5-tzimmermann@suse.de