Fix clearing ZERO_REG
	* config/avr/avr.md (cc): Add alternative "ldi".
	(movqi_insn): Use it in cc attribute.
	* config/avr/avr.c (notice_update_cc): Handle CC_LDI.
	(output_reload_in_const): Use CLR to move 0 to ZERO_REG.
	(output_reload_insisf): Use ZERO_REG to pre-clear register.

From-SVN: r182871