scripts: kernel-doc: add support for typedef enum

scripts: kernel-doc: add support for typedef enum

The PHY kernel-doc markup has gained support for documenting
a typedef enum.

However, right now the parser was not prepared for it.

So, add support for parsing it.

Fixes: 4069a572d423 ("net: phy: Document core PHY structures")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20201117165312.118257-14-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>