ada: Generate host-side CUDA_Register_Function calls for device's adainit/adafinal

ada: Generate host-side CUDA_Register_Function calls for device's adainit/adafinal

To invoke a device-side subprogram from the host (via a CUDA_execute pragma),
the subprogram also has to be registered by calling CUDA_Register_Function.
The host-side adainit and adafinal procedures need to invoke the corresponding
device-side procedures, so corresponding CUDA_Register_Function calls need
to be generated.

gcc/ada/

	* bindgen.adb
	(Gen_CUDA_Init): Move existing loop body into a new local
	procedure, Gen_CUDA_Register_Function_Call, and replace that loop
	body with a call to this procedure. This first part is just
	semantics-preserving refactoring. The second part is to add
	Gen_CUDA_Register_Function_Call calls after the loop for the
	device-side adainit and adafinal procedures.