rtl: use rtx_code for gen_ccmp_first and gen_ccmp_next

Now that we have a forward declaration of rtx_code in coretypes.h, we
can adjust these hooks to take rtx_code arguments rather than an int.

gcc/ChangeLog:

	* target.def (gen_ccmp_first, gen_ccmp_next): Use rtx_code for
	CODE, CMP_CODE and BIT_CODE arguments.
	* config/aarch64/aarch64.cc (aarch64_gen_ccmp_first): Likewise.
	(aarch64_gen_ccmp_next): Likewise.
	* doc/tm.texi: Regenerated.