[RISCV][VLS] Support RISCV VLS calling convention (#100346)

This patch adds a function attribute `riscv_vls_cc` for RISCV VLS
calling
convention which takes 0 or 1 argument, the argument is the `ABI_VLEN`
which is the `VLEN` for passing the fixed-vector arguments, it wraps the
argument as a scalable vector(VLA) using the `ABI_VLEN` and uses the
corresponding mechanism to handle it. The range of `ABI_VLEN` is [32,
65536],
if not specified, the default value is 128.

Here is an example of VLS argument passing:
Non-VLS call:
```
  void original_call(__attribute__((vector_size(16))) int arg) {}
=>
  define void @original_call(i128 noundef %arg) {
  entry:
    ...
    ret void
  }
```
VLS call:
```
  void __attribute__((riscv_vls_cc(256))) vls_call(__attribute__((vector_size(16))) int arg) {}
=>
  define riscv_vls_cc void @vls_call(<vscale x 1 x i32> %arg) {
  entry:
    ...
    ret void
  }
}
```

The first Non-VLS call passes generic vector argument of 16 bytes by
flattened integer.
On the contrary, the VLS call uses `ABI_VLEN=256` which wraps the
vector to <vscale x 1 x i32> where the number of scalable vector
elements
is calaulated by: `ORIG_ELTS * RVV_BITS_PER_BLOCK / ABI_VLEN`.
Note: ORIG_ELTS = Vector Size / Type Size = 128 / 32 = 4.

PsABI PR: https://github.com/riscv-non-isa/riscv-elf-psabi-doc/pull/418
C-API PR: https://github.com/riscv-non-isa/riscv-c-api-doc/pull/68