RISC-V: Refactor Dynamic LMUL codes

RISC-V: Refactor Dynamic LMUL codes

This patch refactor dynamic LMUL to remove this following variable:
static hash_map<class loop *, autovec_info> loop_autovec_infos;

which will keep growing on-the-fly.

gcc/ChangeLog:

	* config/riscv/riscv-vector-costs.cc (get_current_lmul): Remove it.
	(compute_estimated_lmul): New function.
	(costs::costs): Refactor.
	(costs::preferred_new_lmul_p): Ditto.
	(preferred_new_lmul_p): Ditto.
	(costs::better_main_loop_than_p): Ditto.
	* config/riscv/riscv-vector-costs.h (struct autovec_info): Remove it.

gcc/testsuite/ChangeLog:

	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul-mixed-1.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul1-3.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul1-6.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-1.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-2.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-3.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-4.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-5.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-6.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-1.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-2.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-3.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-4.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-5.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-6.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-7.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-8.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-9.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-1.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-10.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-2.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-3.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-4.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-5.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-6.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-7.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-8.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-9.c: Adapt test.
	* gcc.dg/vect/costmodel/riscv/rvv/pr111848.c: Adapt test.