RISC-V: Insert vsetivli zero, 0 for vmv.x.s/vfmv.f.s instructions satisfying REG_P...

RISC-V: Insert vsetivli zero, 0 for vmv.x.s/vfmv.f.s instructions satisfying REG_P(operand[1]) in -O0.

This issue happens is because the operand1 of scalar move can be
REG_P (operand[1]) in the O0 case, which causes the VSETVL PASS to
not insert the vsetvl instruction correctly, and the compiler crashes.

Consider this following case:
int16_t foo1 (void *base, size_t vl)
{
    int16_t maxVal = __riscv_vmv_x_s_i16m1_i16 (__riscv_vle16_v_i16m1 (base, vl));
    return maxVal;
}

Before this patch:
bug.c:15:1: internal compiler error: Segmentation fault
   15 | }
      | ^
0x145d723 crash_signal
	../.././riscv-gcc/gcc/toplev.cc:314
0x22929dd const_csr_operand(rtx_def*, machine_mode)
	../.././riscv-gcc/gcc/config/riscv/predicates.md:44
0x2292a21 csr_operand(rtx_def*, machine_mode)
	../.././riscv-gcc/gcc/config/riscv/predicates.md:46
0x23dfbb0 recog_356
	../.././riscv-gcc/gcc/config/riscv/iterators.md:72
0x23efecd recog(rtx_def*, rtx_insn*, int*)
	../.././riscv-gcc/gcc/config/riscv/iterators.md:89
0xdddc15 recog_memoized(rtx_insn*)
	../.././riscv-gcc/gcc/recog.h:273

After this patch:
	vsetivli	zero,0,e16,m1,ta,ma
	vmv.x.s	a5,v1

gcc/ChangeLog:

	* config/riscv/riscv-vsetvl.cc (gen_vsetvl_pat): For vfmv.f.s/vmv.x.s
	intruction replace null avl with (const_int 0).

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/scalar_move-10.c: New test.
	* gcc.target/riscv/rvv/base/scalar_move-11.c: New test.