RISC-V: Fix ABI vector passing on stack and GPR [PR123824].

RISC-V: Fix ABI vector passing on stack and GPR [PR123824].

Krister reported that we violate the psABI when one vector argument
halfway fits into a register:

"Aggregates whose total size is no more than 2×XLEN bits are passed in a
pair of registers; if only one register is available, the first XLEN
bits are passed in a register and the remaining bits are passed on the
stack. If no registers are available, the aggregate is passed on the
stack."

This patch fixes this oversight and adds a few tests.

Regtested on rv64gcv_zvl512b.

	PR target/123824

gcc/ChangeLog:

	* config/riscv/riscv.cc (riscv_vls_mode_fits_in_gprs_p): New
	helper.
	(riscv_pass_vls_aggregate_in_gpr): Use helper and distribute
	half-fitting vector to GPR and stack.
	(riscv_pass_aggregate_in_vr): Reformat comment.
	(riscv_get_arg_info): Use helper.
	(riscv_pass_by_reference): Ditto.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/abi/vls-gpr-1.c: New test.
	* gcc.target/riscv/abi/vls-gpr-10.c: New test.
	* gcc.target/riscv/abi/vls-gpr-11.c: New test.
	* gcc.target/riscv/abi/vls-gpr-12.c: New test.
	* gcc.target/riscv/abi/vls-gpr-13.c: New test.
	* gcc.target/riscv/abi/vls-gpr-14.c: New test.
	* gcc.target/riscv/abi/vls-gpr-2.c: New test.
	* gcc.target/riscv/abi/vls-gpr-3.c: New test.
	* gcc.target/riscv/abi/vls-gpr-4.c: New test.
	* gcc.target/riscv/abi/vls-gpr-5.c: New test.
	* gcc.target/riscv/abi/vls-gpr-6.c: New test.
	* gcc.target/riscv/abi/vls-gpr-7.c: New test.
	* gcc.target/riscv/abi/vls-gpr-8.c: New test.
	* gcc.target/riscv/abi/vls-gpr-9.c: New test.