drm/i915: Make plane_config->fb a struct drm_framebuffer*

drm/i915: Make plane_config->fb a struct drm_framebuffer*

There's no need to use the intel specific struct intel_framebuffer*
type in the initial plane_config structure. Just make it a
struct drm_framebuffer*.

I think the fewer special types we expose in the interface (even
if just pointers) the better. At least then there is no need to
change the interface definition if we ever change the internal
types. And I hope that the existing examples will generally
encourage people to not expose more special types unless
absolutely necessary.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/20260410150449.9699-5-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>