AVR: Use avr_add_ccclobber / DONE_ADD_CCC in md instead of repeats.

AVR: Use avr_add_ccclobber / DONE_ADD_CCC in md instead of repeats.

There are many post-reload define_insn_and_split's that just append
a  (clobber (reg:CC REG_CC))  to the pattern.  Instead of repeating
the original patterns, avr_add_ccclobber (curr_insn) is used to do
that job.

This avoids repeating patterns all over the place, and splits that do
something different (like using a canonical form) stand out clearly.

gcc/
	* config/avr/avr.md (define_insn_and_split) [reload_completed]:
	For splits that just append a (clobber (reg:CC REG_CC)) to
	the pattern, use avr_add_ccclobber (curr_insn) instead of
	repeating the original pattern.
	* config/avr/avr-dimode.md: Same.
	* config/avr/avr-fixed.md: Same.