drm/i915: simplify dvo dpms interface

All dvo drivers only support 2 dpms states, and our dvo driver
even switches of the dvo port for anything else than DPMS_ON. Hence
ditch this complexity and simply use bool enable.

While reading through this code I've noticed that the mode_set
function of ch7017 is a bit peculiar - it disable the lvds again, even
though the crtc helper code should have done that ... This might be to
work around an issue at driver load, we pretty much ignore the hw
state when taking over.

v2: Also do the conversion for the new ns2501 driver.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/dvo_sil164.c

@@ -208,7 +208,7 @@ static void sil164_mode_set(struct intel_dvo_device *dvo,
 }
 
 /* set the SIL164 power state */
-static void sil164_dpms(struct intel_dvo_device *dvo, int mode)
+static void sil164_dpms(struct intel_dvo_device *dvo, bool enable)
 {
 	int ret;
 	unsigned char ch;
@@ -217,7 +217,7 @@ static void sil164_dpms(struct intel_dvo_device *dvo, int mode)
 	if (ret == false)
 		return;
 
-	if (mode == DRM_MODE_DPMS_ON)
+	if (enable)
 		ch |= SIL164_8_PD;
 	else
 		ch &= ~SIL164_8_PD;