hard-code 'mlir-aie' as the package prefix and '8.3' as the version

[andrej]

This would allow us to use this repository in requirements.txt without setting HOST_MLIR_PYTHON_PREFIX etc., for a cleaner user experience:

For example, for AMD/Iron, before:

Install required Python packages (from requirements.txt):

MLIR_PYTHON_EXTRAS_SET_VERSION="0.0.8.3" HOST_MLIR_PYTHON_PACKAGE_PREFIX="aie" pip install -r requirements.txt

after:

Install required Python packages (from requirements.txt):

pip install -r requirements.txt

If preferred, you could just put this on a branch too.