opencv: Add libeigen dependency

In the opencv's CMakeLists.txt under Optional 3rd party components,
the option "WITH_EIGEN" is by default ON. Hence, this commit adds
the libeigen dependency to opencv.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@oss.bmw-carit.de>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>