scripts: get_abi.pl: detect duplicated ABI definitions

The ABI should define only once each What. The current script
logic assumes that.

However, that's not the case, currently: there are several
symbols with a generic definition, and per-driver ones.

Better handle such cases, by preserving the cross-references
with the files that define them, but also track such
cases, producing warnings, as they should be fixed.

Acked-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/d7a73b8b3aae5b2bff9279996ff9ca4cdfc89196.1604042072.git.mchehab+huawei@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>