LoongArch Port: Machine description files.

2022-03-29  Chenghua Xu  <xuchenghua@loongson.cn>
	    Lulu Cheng  <chenglulu@loongson.cn>

gcc/ChangeLog:

	* config/loongarch/constraints.md: New file.
	* config/loongarch/generic.md: New file.
	* config/loongarch/la464.md: New file.
	* config/loongarch/loongarch-ftypes.def: New file.
	* config/loongarch/loongarch-modes.def: New file.
	* config/loongarch/loongarch.md: New file.
	* config/loongarch/predicates.md: New file.
	* config/loongarch/sync.md: New file.