drm/i915: move i915_fixed.h to display/intel_fixed.h

All the users are in display, move the fixed point header under
display. We could also consider making these more general purpose
things, but that takes a bunch more effort. This allows the immediate
cleanup of xe compat i915_fixed.h.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/320c451e116c7807e544a50c67ba79b087a4f218.1712345787.git.jani.nikula@intel.comSigned-off-by: Jani Nikula <jani.nikula@intel.com>

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

@@ -6,7 +6,6 @@
 #include <drm/drm_blend.h>
 
 #include "i915_drv.h"
-#include "i915_fixed.h"
 #include "i915_reg.h"
 #include "i9xx_wm.h"
 #include "intel_atomic.h"
@@ -19,6 +18,7 @@
 #include "intel_display_power.h"
 #include "intel_display_types.h"
 #include "intel_fb.h"
+#include "intel_fixed.h"
 #include "intel_pcode.h"
 #include "intel_wm.h"
 #include "skl_watermark.h"

drivers/gpu/drm/xe/compat-i915-headers/i915_fixed.h

-/* SPDX-License-Identifier: MIT */
-/*
- * Copyright © 2023 Intel Corporation
- */
-
-#include "../../i915/i915_fixed.h"