This PR adds support for complex power operations (`cpow`) in the
`ComplexToROCDLLibraryCalls` conversion pass, specifically targeting
AMDGPU architectures. The implementation optimises complex
exponentiation by using mathematical identities and special-case
handling for small integer powers.
- Force lowering to `complex.pow` operations for the `amdgcn-amd-amdhsa`
target instead of using library calls
- Convert `complex.pow(z, w)` to `complex.exp(w * complex.log(z))` using
mathematical identity
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