drm/i915: Clean up ADPA pipe select bits

Clean up the ADPA pipe select bits. To make the whole situation a bit
less ugly we'll start to share the same code between .get_hw_state()
and the port state asserts.

v2: Order the defines shift,mask,value (Jani)

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180514172423.9302-1-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/intel_drv.h

@@ -1377,6 +1377,8 @@ void gen9_enable_guc_interrupts(struct drm_i915_private *dev_priv);
 void gen9_disable_guc_interrupts(struct drm_i915_private *dev_priv);
 
 /* intel_crt.c */
+bool intel_crt_port_enabled(struct drm_i915_private *dev_priv,
+			    i915_reg_t adpa_reg, enum pipe *pipe);
 void intel_crt_init(struct drm_i915_private *dev_priv);
 void intel_crt_reset(struct drm_encoder *encoder);