[Patch AArch64] Reinstate CANNOT_CHANGE_MODE_CLASS to fix pr67609

[Patch AArch64] Reinstate CANNOT_CHANGE_MODE_CLASS to fix pr67609

gcc/

	PR rtl-optimization/67609
	* config/aarch64/aarch64-protos.h
	(aarch64_cannot_change_mode_class): Bring back.
	* config/aarch64/aarch64.c
	(aarch64_cannot_change_mode_class): Likewise.
	* config/aarch64/aarch64.h (CANNOT_CHANGE_MODE_CLASS): Likewise.
	* config/aarch64/aarch64.md (aarch64_movdi_<mode>low): Use
	zero_extract rather than truncate.
	(aarch64_movdi_<mode>high): Likewise.

gcc/testsuite/

	PR rtl-optimization/67609
	* gcc.dg/torture/pr67609.c: New.

From-SVN: r231455