media: staging: ipu3-imgu: Move the UAPI header from include under include/uapi

The header defines the user space interface but may be mistaken as
kernel-only header due to its location. Add "uapi" directory under
driver's include directory and move the header there.

Suggested-by: Greg KH <gregkh@linuxfoundation.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Bingbu Cao <bingbu.cao@intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>