RISC-V: Fix SUBREG move of VLS mode[PR111486]

RISC-V: Fix SUBREG move of VLS mode[PR111486]

This patch fixes this bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111486

Before this patch, we can only handle (subreg:DI (reg:V8QI))

The PR ICE:

during RTL pass: reload
testcase.c: In function 'foo':
testcase.c:8:1: internal compiler error: in require, at machmode.h:313
    8 | }
      | ^
0xa40cd2 opt_mode<machine_mode>::require() const
        /repo/gcc-trunk/gcc/machmode.h:313
0xa47091 opt_mode<machine_mode>::require() const
        /repo/gcc-trunk/gcc/config/riscv/riscv.cc:2546
0xa47091 riscv_legitimize_move(machine_mode, rtx_def*, rtx_def*)
        /repo/gcc-trunk/gcc/config/riscv/riscv.cc:2543
0x1f1df10 gen_movdi(rtx_def*, rtx_def*)
        /repo/gcc-trunk/gcc/config/riscv/riscv.md:2024
0x10f1423 rtx_insn* insn_gen_fn::operator()<rtx_def*, rtx_def*>(rtx_def*, rtx_def*) const
        /repo/gcc-trunk/gcc/recog.h:411
0x10f1423 emit_move_insn_1(rtx_def*, rtx_def*)
        /repo/gcc-trunk/gcc/expr.cc:4164
0x10f183d emit_move_insn(rtx_def*, rtx_def*)
        /repo/gcc-trunk/gcc/expr.cc:4334
0x13070ec lra_emit_move(rtx_def*, rtx_def*)
        /repo/gcc-trunk/gcc/lra.cc:509
0x132295b curr_insn_transform
        /repo/gcc-trunk/gcc/lra-constraints.cc:4748
0x1324335 lra_constraints(bool)
        /repo/gcc-trunk/gcc/lra-constraints.cc:5488
0x130a3d4 lra(_IO_FILE*)
        /repo/gcc-trunk/gcc/lra.cc:2419
0x12bb629 do_reload
        /repo/gcc-trunk/gcc/ira.cc:5970
0x12bb629 execute
        /repo/gcc-trunk/gcc/ira.cc:6156

Because of (subreg:DI (reg:V2QI))

	PR target/111486

gcc/ChangeLog:

	* config/riscv/riscv.cc (riscv_legitimize_move): Fix bug.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/pr111486.c: New test.