AVR: Allow more combinations of XOR / IOR with byte-shifts.

AVR: Allow more combinations of XOR / IOR with byte-shifts.

This patch takes some existing patterns that have QImode as one
input and uses a mode iterator to allow for more modes to match.
These insns are split after reload into *xorqi3 resp. *iorqi3 insn(s).

gcc/
	* config/avr/avr-protos.h (avr_emit_xior_with_shift): New proto.
	* config/avr/avr.cc (avr_emit_xior_with_shift): New function.
	* config/avr/avr.md (any_lshift): New code iterator.
	(*<xior:code><mode>.<any_lshift:code>): New insn-and-split.
	(<code><HISI:mode><QIPSI:mode>.0): Replaces...
	(*<code_stdname><mode>qi.byte0): ...this one.
	(*<xior:code><HISI:mode><QIPSI:mode>.<any_lshift:code>): Replaces...
	(*<code_stdname><mode>qi.byte1-3): ...this one.