scripts/lib/kdoc/kdoc_parser.py: move states to a separate class

scripts/lib/kdoc/kdoc_parser.py: move states to a separate class

States are really enums. on Python, enums are actually classes,
as can be seen at:
	https://docs.python.org/3/library/enum.html

Yet, I can't see any advantage of derivating the class from
enum class here. So, just place the states on a separate class.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/00cb4e0b8a1545bf7c4401b58213841db5cba2e2.1744685912.git.mchehab+huawei@kernel.org