drm/i915/reg: split out icl_dsi_regs.h

The ICL DSI registers have fairly isolated usage. Split the register
macros to a separate file.

Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220217224023.3994777-4-jani.nikula@intel.com

drivers/gpu/drm/i915/display/icl_dsi.c

@@ -29,6 +29,7 @@
 #include <drm/drm_mipi_dsi.h>
 
 #include "icl_dsi.h"
+#include "icl_dsi_regs.h"
 #include "intel_atomic.h"
 #include "intel_backlight.h"
 #include "intel_combo_phy.h"

drivers/gpu/drm/i915/i915_irq.c

@@ -34,6 +34,7 @@
 
 #include <drm/drm_drv.h>
 
+#include "display/icl_dsi_regs.h"
 #include "display/intel_de.h"
 #include "display/intel_display_trace.h"
 #include "display/intel_display_types.h"