drm/i915/fb: convert intel_fb_bo_framebuffer_fini() to struct drm_i915_gem_object

drm/i915/fb: convert intel_fb_bo_framebuffer_fini() to struct drm_i915_gem_object

Prefer the driver agnostic struct drm_gem_object over i915 specific
struct drm_i915_gem_object.

The xe specific intel_fb_bo.h becomes redundant. Remove it, and rely on
the common header in i915 display.

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/0efbc9ae2dbe157f92fa71d423ed37fd17346da5.1726589119.git.jani.nikula@intel.com