drm/xe/display: Avoid calling readq()

readq() is not available in 32bits and i915_gem_object_read_from_page()
is supposed to allow reading arbitrary sizes determined by the `size`
argument. Currently the only caller only passes a size == 8 so the
second problem is not that big. Migrate to calling
memcpy()/memcpy_fromio() to allow possible changes in the display side
and to fix the build on 32b architectures.

v2: Use memcpy/memcpy_fromio directly rather than using iosys-map with
    the same size == 8 bytes restriction (Matt Roper)

Fixes: 44e69495 ("drm/xe/display: Implement display support")
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240119001612.2991381-4-lucas.demarchi@intel.com

drivers/gpu/drm/xe/compat-i915-headers/gem/i915_gem_object.h

@@ -35,12 +35,10 @@ static inline int i915_gem_object_read_from_page(struct xe_bo *bo,
 					  u32 ofs, u64 *ptr, u32 size)
 {
 	struct ttm_bo_kmap_obj map;
-	void *virtual;
+	void *src;
 	bool is_iomem;
 	int ret;
 
-	XE_WARN_ON(size != 8);
-
 	ret = xe_bo_lock(bo, true);
 	if (ret)
 		return ret;
@@ -50,11 +48,12 @@ static inline int i915_gem_object_read_from_page(struct xe_bo *bo,
 		goto out_unlock;
 
 	ofs &= ~PAGE_MASK;
-	virtual = ttm_kmap_obj_virtual(&map, &is_iomem);
+	src = ttm_kmap_obj_virtual(&map, &is_iomem);
+	src += ofs;
 	if (is_iomem)
-		*ptr = readq((void __iomem *)(virtual + ofs));
+		memcpy_fromio(ptr, (void __iomem *)src, size);
 	else
-		*ptr = *(u64 *)(virtual + ofs);
+		memcpy(ptr, src, size);
 
 	ttm_bo_kunmap(&map);
 out_unlock: