[mlir][linalg] Use arrays to pass padding options.

[mlir][linalg] Use arrays to pass padding options.

Pass the padding options using arrays instead of lambdas. In particular pass the padding value as string and use the argument parser to create the padding value. Arrays are a more natural choice that matches the current use cases and avoids converting arrays to lambdas.

Reviewed By: nicolasvasilache

Differential Revision: https://reviews.llvm.org/D122309