scripts: kernel-doc: split typedef complex regex

The typedef regex for function prototypes are very complex.
Split them into 3 separate regex and then join them using
qr.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/3a4af999a0d62d4ab9dfae1cdefdfcad93383356.1603792384.git.mchehab+huawei@kernel.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>