bxe: tag files to skip clang-format formatting

bxe contains three files which are sets of constants or other data, and
might be auto-generated or have an upstream. They are rather large
files and clang-format takes quite some time when run against them, so
just skip formatting.

MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D27806

(cherry picked from commit c3295781fd5d58b6de2a2e0360b0b67b94dde1ff)