[compiler] Integrate xDSL kernel compilation into IREE

[zero9178]

This PR contains the initial version integrating xDSL with IREE. The steps performed are the following:

• Split a kernel function into two:
  • A pure MLIR dialects module that will be compiled by xDSL
  • A trampoline containing HAL operations that calls the latter
• Compile the pure MLIR functions with xDSL to an object file
• Compile the trampoline using IREE's lowerings and LLVM to an object file
• Combine all object files into a single object file
• Output a static library the same way the LLVMCPU target does

This introduces two new build dependencies:

• xdsl-opt for kernel compilation
• The pulp-toolchain to assemble the output from xDSL