RISC-V: Eliminate redundant vsetvli for duplicate AVL def

RISC-V: Eliminate redundant vsetvli for duplicate AVL def

This patch is the V2 patch:https://patchwork.sourceware.org/project/gcc/patch/20230328010124.235703-1-juzhe.zhong@rivai.ai/

Address comments from Jeff. Add comments for all_avail_in_compatible_p and refine comments of codes.

gcc/ChangeLog:

	* config/riscv/riscv-vsetvl.cc
	(vector_infos_manager::all_avail_in_compatible_p): New function.
	(pass_vsetvl::refine_vsetvls): Optimize vsetvls.
	* config/riscv/riscv-vsetvl.h: New function.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/vsetvl/avl_single-102.c: New test.