RISC-V: The vtype immediate with more than the defined 8 bits are preserved.

According the rvv spec,
https://github.com/riscv/riscv-v-spec/blob/master/vtype-format.adoc

The bits of vtype immediate from 8 to (xlen - 1) should be reserved.
Therefore, we should also dump the vtype immediate as numbers, when
they are set over 8-bits.  I think this is a bug that we used to support
vediv extension and use the bit 8 and 9 of vtype, but forgot to update
the behavior when removing the vediv.

Consider the testcases,

vsetvli  a0, a1,  0x700    # the reserved bit 10, 9 and 8 are used.
vsetvli  a0, a1,  0x400    # the reserved bit 10 is used.
vsetvli  a0, a1,  0x300    # the reserved bit 9 and 8 are used.
vsetvli  a0, a1,  0x100    # the reserved bit 8 is used.
vsetivli a0, 0xb, 0x300    # the reserved bit 9 and 8 are used.
vsetivli a0, 0xb, 0x100    # the reserved bit 8 is used.

The original objdump shows the following result,

0000000000000000 <.text>:
   0:   7005f557                vsetvli a0,a1,1792
   4:   4005f557                vsetvli a0,a1,1024
   8:   3005f557                vsetvli a0,a1,e8,m1,tu,mu
   c:   1005f557                vsetvli a0,a1,e8,m1,tu,mu
  10:   f005f557                vsetivli        a0,11,e8,m1,tu,mu
  14:   d005f557                vsetivli        a0,11,e8,m1,tu,mu

But in fact the correct result should be,

0000000000000000 <.text>:
   0:   7005f557                vsetvli a0,a1,1792
   4:   4005f557                vsetvli a0,a1,1024
   8:   3005f557                vsetvli a0,a1,768
   c:   1005f557                vsetvli a0,a1,256
  10:   f005f557                vsetivli        a0,11,768
  14:   d005f557                vsetivli        a0,11,256

gas/
	* testsuite/gas/riscv/vector-insns.d: Added testcases to
	test the reserved bit 8 to (xlen-1) of vtype.
	* testsuite/gas/riscv/vector-insns.s: Likewise.
include/
	* opcode/riscv.h: Removed OP_MASK_VTYPE_RES and OP_SH_VTYPE_RES,
	since they are different for operand Vc and Vb.
opcodes/
	* riscv-dis.c (print_insn_args): Updated imm_vtype_res to
	extract the reserved immediate of vtype correctly.

include/opcode/riscv.h

@@ -306,8 +306,6 @@ static const char * const riscv_pred_succ[16] =
 #define OP_SH_VTA		6
 #define OP_MASK_VMA		0x1
 #define OP_SH_VMA		7
-#define OP_MASK_VTYPE_RES	0x1
-#define OP_SH_VTYPE_RES		10
 #define OP_MASK_VWD		0x1
 #define OP_SH_VWD		26