RISC-V: Some minior tweak on dynamic LMUL cost model

RISC-V: Some minior tweak on dynamic LMUL cost model

Tweak some codes of dynamic LMUL cost model to make computation more predictable and accurate.

Tested on both RV32 and RV64 no regression.

Committed.

	PR target/113112

gcc/ChangeLog:

	* config/riscv/riscv-vector-costs.cc (compute_estimated_lmul): Tweak LMUL estimation.
	(has_unexpected_spills_p): Ditto.
	(costs::record_potential_unexpected_spills): Ditto.

gcc/testsuite/ChangeLog:

	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul1-1.c: Add more checks.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul1-2.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul1-3.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul1-4.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul1-5.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul1-6.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul1-7.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-1.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-2.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-3.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-4.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-5.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-1.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-2.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-3.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-5.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-6.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-7.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-8.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-1.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-10.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-11.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-2.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-3.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-4.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-5.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-6.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-7.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-8.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-9.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-12.c: New test.
	* gcc.dg/vect/costmodel/riscv/rvv/pr113112-2.c: New test.