drm/i915: Remove leftover intel_sprite_set_colorkey_ioctl() prototype

drm/i915: Remove leftover intel_sprite_set_colorkey_ioctl() prototype

intel_sprite_set_colorkey_ioctl() lives in intel_sprice_uapi.{c,h}
these days. For some reason the old protoype was left behind
in intel_sprite.h and even used by i915_driver.c. Remove the
leftovers and switch to including the correct header for the
prototype.

v2: Drop more unnecessary forward declarations

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240916162413.8555-2-ville.syrjala@linux.intel.com
Reviewed-by: Vinod Govindapillai <vinod.govindapillai@intel.com>