drm/i915: rewrite the LCPLL code

Right now, we're trying to enable LCPLL at every mode set, but we're
never disabling it. Also, we really don't want to be disabling LCPLL
since it requires a very complex disable/enable sequence. This
register should really be set by the BIOS and we shouldn't be touching
it. Still, let's try to check its value and print some errors in case
we find something wrong. We're also adding intel_ddi_get_cdclk_freq
which will be used later in other places.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 79f8ed6..57566b7 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -580,5 +580,6 @@
 extern void intel_ddi_mode_set(struct drm_encoder *encoder,
 				struct drm_display_mode *mode,
 				struct drm_display_mode *adjusted_mode);
+extern void intel_ddi_pll_init(struct drm_device *dev);
 
 #endif /* __INTEL_DRV_H__ */