dev-libs/efl seems to be the only package in the tree naming this flag v4l2, while all others name it v4l, It neither appears offers any choice v4l1 vs. v4l2, so the appended 2 seems to be superfluous.
thanks, renamed now: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=116c5948ceffcc4f08e8cbb610e18a87c355a6bc