AVR: target/120856 - Deny R24:DI in avr_hard_regno_mode_ok with Reload.

AVR: target/120856 - Deny R24:DI in avr_hard_regno_mode_ok with Reload.

This fixes an ICE with -mno-lra when split2 tries to split the following
zero_extendsidi2 insn:

   (set (reg:DI 24)
        (zero_extend:DI (reg:SI **)))

The ICE is because avr_hard_regno_mode_ok allows R24:DI but disallows
R28:SI when Reload is used.  R28:SI is a result of zero_extendsidi2.

This ICE only occurs with Reload (which will die before very long),
but it occurs when building libgcc.

gcc/
	PR target/120856
	* config/avr/avr.cc (avr_hard_regno_mode_ok) [-mno-lra]: Deny
	hard regs >= 4 bytes that overlap Y.