Add pyproject.toml to describe swig dependency

Previous setup.py change only works for python
v3.12, however basing on our testing the toml fix
can works for v3.8~v3.12

According to above reason, add pyproject.toml file
to describe all the dependency without modifying
setup.py

This also reverts previous commit
"Add swig dependency":
b980a27.

Signed-off-by: Chasel Chiu <chasel.chiu@intel.com>

pyproject.toml

@@ -0,0 +1,3 @@
+[build-system]
+requires = ["setuptools","setuptools_scm","swig"]
+build-backend = "setuptools.build_meta"

setup.py

@@ -44,13 +44,13 @@ def run(self):
     name='pylibfdt',
     cmdclass = {'build_py' : build_py},
     use_scm_version=True,
-    setup_requires = ['setuptools_scm', 'swig'],
+    setup_requires = ['setuptools_scm'],
     author='Simon Glass <sjg@chromium.org>',
     description='Python binding for libfdt',
     ext_modules=[libfdt_module],
     py_modules=['libfdt'],
     package_dir={'': 'libfdt'},
-    python_requires=">=3.8",
+
     long_description=long_description,
     long_description_content_type="text/plain",
 )