[PowerPC] Replace vspltisw+vadduwm instructions with xxleqv+vsubuwm for adding the vector {1, 1, 1, 1} (#160882)

This patch optimizes vector addition operations involving **`all-ones`**
vectors by leveraging the generation of vectors of -1s(using `xxleqv`,
which is cheaper than generating vectors of 1s(`vspltisw`). These are
the respective vector types.
`v2i64`: **`A + vector {1, 1}`**
`v4i32`: **`A + vector {1, 1, 1, 1}`**
`v8i16`: **`A + vector {1, 1, 1, 1, 1, 1, 1, 1}`**
`v16i8`: **`A + vector {1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1}`**

The optimized version replaces `vspltisw (4 cycles)` with `xxleqv (2
cycles)` using the following identity:
`A - (-1) = A + 1`.

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Co-authored-by: himadhith <himadhith.v@ibm.com>
Co-authored-by: Tony Varghese <tonypalampalliyil@gmail.com>

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