scripts/lib/kdoc/kdoc_parser.py: move kernel entry to a class

The KernelDoc class is too complex. Start optimizing it by
placing the kernel-doc parser entry to a separate class.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <28b456f726a022011f0ce5810dbcc26827c1403a.1745564565.git.mchehab+huawei@kernel.org>

Author: mchehab