configure: add missing avx2 support check

AVX2 support was introduced in Yasm 1.2.0 and NASM 2.10, and the
oldest versions currently supported are Yasm 0.8.0 and NASM 2.03

Signed-off-by: James Almer <jamrial@gmail.com>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>