aarch64: Register rng builtins with uint64_t pointers.

Currently, these are registered as unsigned_intDI_type_node which is not
necessarily the same type definition as uint64_t.  On platforms where these
differ that causes fails in consuming the arm_acle.h header.

gcc/ChangeLog:

	* config/aarch64/aarch64-builtins.cc (aarch64_init_rng_builtins):
	Register these builtins with a pointer to uint64_t rather than unsigned
	DI mode.