scripts/get_abi.pl: represent what in tables

Several entries at the ABI have multiple What: with the same
description.

Instead of showing those symbols as sections, let's show them
as tables. That makes easier to read on the final output,
and avoid too much recursion at Sphinx parsing.

We need to put file references at the end, as we don't want
non-file tables to be mangled with other entries.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>