AVR: Refactor avr.cc::out_shift_with_cnt().

AVR: Refactor avr.cc::out_shift_with_cnt().

This is a no-op refactoring of out_shift_with_cnt() that passes the
shift rtx_code instead of an template asm string.

gcc/
	* config/avr/avr-protos.h (out_shift_with_cnt): Remove.
	* config/avr/avr.cc (avr_out_shift_with_cnt): New static
	function from out_shift_with_cnt: Pass shift rtx_code instead
	of asm template.
	(avr_out_shift_1): New static helper function.
	(ashlqi3_out, ashlhi3_out, avr_out_ashlpsi3, ashlsi3_out)
	(ashrqi3_out, ashrhi3_out, avr_out_ashrpsi3, ashrsi3_out)
	(lshrqi3_out, lshrhi3_out, avr_out_lshrpsi3, lshrsi3_out):
	Adjust avr_out_shift_with_cnt to new interface.