RISC-V: Bugfix for rvv bool mode precision adjustment

Fix the bug of the rvv bool mode precision with the adjustment.
The bits size of vbool*_t will be adjusted to
[1, 2, 4, 8, 16, 32, 64] according to the rvv spec 1.0 isa. The
adjusted mode precison of vbool*_t will help underlying pass to
make the right decision for both the correctness and optimization.

Given below sample code:

void test_1(int8_t * restrict in, int8_t * restrict out)
{
  vbool8_t v2 = *(vbool8_t*)in;
  vbool16_t v5 = *(vbool16_t*)in;
  *(vbool16_t*)(out + 200) = v5;
  *(vbool8_t*)(out + 100) = v2;
}

Before the precision adjustment:

addi    a4,a1,100
vsetvli a5,zero,e8,m1,ta,ma
addi    a1,a1,200
vlm.v   v24,0(a0)
vsm.v   v24,0(a4)
// Need one vsetvli and vlm.v for correctness here.
vsm.v   v24,0(a1)

After the precision adjustment:

csrr    t0,vlenb
slli    t1,t0,1
csrr    a3,vlenb
sub     sp,sp,t1
slli    a4,a3,1
add     a4,a4,sp
sub     a3,a4,a3
vsetvli a5,zero,e8,m1,ta,ma
addi    a2,a1,200
vlm.v   v24,0(a0)
vsm.v   v24,0(a3)
addi    a1,a1,100
vsetvli a4,zero,e8,mf2,ta,ma
csrr    t0,vlenb
vlm.v   v25,0(a3)
vsm.v   v25,0(a2)
slli    t1,t0,1
vsetvli a5,zero,e8,m1,ta,ma
vsm.v   v24,0(a1)
add     sp,sp,t1
jr      ra

However, there may be some optimization opportunates after
the mode precision adjustment. It can be token care of in
the RISC-V backend in the underlying separted PR(s).

gcc/ChangeLog:

	PR target/108185
	PR target/108654
	* config/riscv/riscv-modes.def (ADJUST_PRECISION): Adjust VNx*BI
	modes.
	* config/riscv/riscv.cc (riscv_v_adjust_precision): New.
	* config/riscv/riscv.h (riscv_v_adjust_precision): New.
	* genmodes.cc (adj_precision): New.
	(ADJUST_PRECISION): New.
	(emit_mode_adjustments): Handle ADJUST_PRECISION.

gcc/testsuite/ChangeLog:

	PR target/108185
	PR target/108654
	* gcc.target/riscv/rvv/base/pr108185-1.c: New test.
	* gcc.target/riscv/rvv/base/pr108185-2.c: New test.
	* gcc.target/riscv/rvv/base/pr108185-3.c: New test.
	* gcc.target/riscv/rvv/base/pr108185-4.c: New test.
	* gcc.target/riscv/rvv/base/pr108185-5.c: New test.
	* gcc.target/riscv/rvv/base/pr108185-6.c: New test.
	* gcc.target/riscv/rvv/base/pr108185-7.c: New test.
	* gcc.target/riscv/rvv/base/pr108185-8.c: New test.

Signed-off-by: Pan Li <pan2.li@intel.com>
Co-authored-by: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>