drm/i915: Fix port_clock and adjusted_mode.clock readout all over

Now that adjusted_mode.clock no longer contains the pixel_multiplier, we
can kill the get_clock() callback and instead do the clock readout
in get_pipe_config().

Also i9xx_crtc_clock_get() can now extract the frequency of the PCH
DPLL, so use it to populate port_clock accurately for PCH encoders.
For DP in port A the encoder is still responsible for filling in
port_clock. The FDI adjusted_mode.clock extraction is kept in place
for some extra sanity checking, but we no longer need to pretend it's
also the port_clock.

In the encoder get_config() functions fill out adjusted_mode.clock
based on port_clock and other details such as the DP M/N values,
HDMI 12bpc and SDVO pixel_multiplier. For PCH encoders we will then
do an extra sanity check to make sure the dotclock we derived from
the FDI configuratiuon matches the one we derive from port_clock.

DVO doesn't exist on PCH platforms, so it doesn't need to anything
but assign adjusted_mode.clock=port_clock. And DDI is HSW only, so
none of the changes apply there.

v2: Use hdmi_reg color format to detect 12bpc HDMI case
v3: Set adjusted_mode.clock for LVDS too
v4: Rename ironlake_crtc_clock_get to ironlake_pch_clock_get,
    eliminate the useless link_freq variable.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@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 9360694..e87ba82 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -805,5 +805,7 @@
 			     struct intel_crtc_config *pipe_config);
 extern int intel_dotclock_calculate(int link_freq,
 				    const struct intel_link_m_n *m_n);
+extern void ironlake_check_encoder_dotclock(const struct intel_crtc_config *pipe_config,
+					    int dotclock);
 
 #endif /* __INTEL_DRV_H__ */