opencv_3.4.bbappend

FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
FILES_${PN} += "${libdir}/python3.5/site-packages/cv2.so"
INSANE_SKIP_${PN} += "dev-so"

python() {
    value = "eigen python3 " + d.getVar('PACKAGECONFIG', True)
    flags = d.getVarFlags('PACKAGECONFIG')
    d.delVar('PACKAGECONFIG')
    d.setVar('PACKAGECONFIG', value)
    d.setVarFlags('PACKAGECONFIG', flags)
}

do_install_append() {
    # Create missing symlink needed to import cv2 Python module
    cd ${D}/${libdir}/python3.5/site-packages
    ln -s cv2.cpython-35m-aarch64-linux-gnu.so cv2.so
}

Got a lot of QA warnings while trying to build this:

WARNING: Duplicate inclusion for /jenkins/workspace/ivs/sources/meta-openembedded/meta-networking/conf/distro/include/meta_networking_security_flags.inc in /jenkins/workspace/ivs/sources/meta-openembedded/meta-networking/conf/layer.conf
NOTE: Executing RunQueue Tasks
WARNING: opencv-3.4+gitAUTOINC+6d4f66472e_81ca8dab86_a62e20676a_34e4206aef_fccf7cd6a4-r0 do_configure: QA Issue: opencv: invalid PACKAGECONFIG: eigen [invalid-packageconfig]
WARNING: opencv-3.4+gitAUTOINC+6d4f66472e_81ca8dab86_a62e20676a_34e4206aef_fccf7cd6a4-r0 do_configure: QA Issue: opencv: invalid PACKAGECONFIG: python3 [invalid-packageconfig]
WARNING: opencv-3.4+gitAUTOINC+6d4f66472e_81ca8dab86_a62e20676a_34e4206aef_fccf7cd6a4-r0 do_configure: QA Issue: opencv: invalid PACKAGECONFIG: jpeg [invalid-packageconfig]
WARNING: opencv-3.4+gitAUTOINC+6d4f66472e_81ca8dab86_a62e20676a_34e4206aef_fccf7cd6a4-r0 do_configure: QA Issue: opencv: invalid PACKAGECONFIG: png [invalid-packageconfig]
WARNING: opencv-3.4+gitAUTOINC+6d4f66472e_81ca8dab86_a62e20676a_34e4206aef_fccf7cd6a4-r0 do_configure: QA Issue: opencv: invalid PACKAGECONFIG: tiff [invalid-packageconfig]
WARNING: opencv-3.4+gitAUTOINC+6d4f66472e_81ca8dab86_a62e20676a_34e4206aef_fccf7cd6a4-r0 do_configure: QA Issue: opencv: invalid PACKAGECONFIG: v4l [invalid-packageconfig]
WARNING: opencv-3.4+gitAUTOINC+6d4f66472e_81ca8dab86_a62e20676a_34e4206aef_fccf7cd6a4-r0 do_configure: QA Issue: opencv: invalid PACKAGECONFIG: libv4l [invalid-packageconfig]
WARNING: opencv-3.4+gitAUTOINC+6d4f66472e_81ca8dab86_a62e20676a_34e4206aef_fccf7cd6a4-r0 do_configure: QA Issue: opencv: invalid PACKAGECONFIG: gstreamer [invalid-packageconfig]
WARNING: opencv-3.4+gitAUTOINC+6d4f66472e_81ca8dab86_a62e20676a_34e4206aef_fccf7cd6a4-r0 do_configure: QA Issue: opencv: invalid PACKAGECONFIG: samples [invalid-packageconfig]
WARNING: opencv-3.4+gitAUTOINC+6d4f66472e_81ca8dab86_a62e20676a_34e4206aef_fccf7cd6a4-r0 do_configure: QA Issue: opencv: invalid PACKAGECONFIG: tbb [invalid-packageconfig]
WARNING: opencv-3.4+gitAUTOINC+6d4f66472e_81ca8dab86_a62e20676a_34e4206aef_fccf7cd6a4-r0 do_configure: QA Issue: opencv: invalid PACKAGECONFIG: gphoto2 [invalid-packageconfig]
WARNING: opencv-3.4+gitAUTOINC+6d4f66472e_81ca8dab86_a62e20676a_34e4206aef_fccf7cd6a4-r0 do_configure: QA Issue: opencv: invalid PACKAGECONFIG: opencl [invalid-packageconfig]

Oh, I should mention that the append shown above is an attempt to 'undo' this line from meta-fsl-bsp-release/imx/meta-bsp/recipes-graphics/opencv/opencv_3.4.bbappend:

PACKAGECONFIG_remove_imx   = "eigen python3"

Apparently, it is really difficult to undo this removal syntax!

FWIW, this didn't actually work in my particular use case.