configs/orangepi_one_plus: new defconfig

Add initial support for Orangepi One Plus board with below features:

- U-Boot 2018.09
- Linux 4.19.0-rc8
- Default packages from buildroot

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>