drm/i915/cx0: prefer forward declarations over includes

Avoid including the world from headers when forward declarations
suffice.

Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230921155325.3851197-1-jani.nikula@intel.com

drivers/gpu/drm/i915/display/intel_cx0_phy.h

@@ -10,14 +10,15 @@
 #include <linux/bitfield.h>
 #include <linux/bits.h>
 
-#include "i915_drv.h"
-#include "intel_display_types.h"
-
-struct drm_i915_private;
-struct intel_encoder;
-struct intel_crtc_state;
 enum icl_port_dpll_id;
 enum phy;
+struct drm_i915_private;
+struct intel_atomic_state;
+struct intel_c10pll_state;
+struct intel_c20pll_state;
+struct intel_crtc_state;
+struct intel_encoder;
+struct intel_hdmi;
 
 bool intel_is_c10phy(struct drm_i915_private *dev_priv, enum phy phy);
 void intel_mtl_pll_enable(struct intel_encoder *encoder,
@@ -44,4 +45,5 @@ void intel_cx0_phy_set_signal_levels(struct intel_encoder *encoder,
 				     const struct intel_crtc_state *crtc_state);
 int intel_cx0_phy_check_hdmi_link_rate(struct intel_hdmi *hdmi, int clock);
 int intel_mtl_tbt_calc_port_clock(struct intel_encoder *encoder);
+
 #endif /* __INTEL_CX0_PHY_H__ */