1. Drop workarounds for GCC 8.x
2. Provide eMMC as env variable, which is used in extlinux.conf
distroboot script.
3. Use default defconfig for all arm64.
4. Merge additional poplar.conf

Acked-by: Jerome Forissier <jerome@forissier.org>
Signed-off-by: Igor Opaniuk <igor.opaniuk@gmail.com>