Add a pattern for better popcount detection.

Ok for master?

Johann

--

AVR: target/114975 - Add combine-pattern for __popcountqi2.

	PR target/114975
gcc/
	* config/avr/avr.md: Add combine pattern for
	8-bit popcount detection.

gcc/testsuite/
	* gcc.target/avr/pr114975-popcount.c: New test.