board/orangepi: add support for orangepi-pc-plus board

This board is a variant of orangepi-pc board. It adds 8GB eMMC and Realtek
RTL8189FTV SDIO WiFi chip. This variant has a separate support in U-Boot
and kernel. So it makes sense to create a separate entry
for this board in buildroot.

Board support package includes the following components:
 - mainline u-boot 2017.09
 - mainline kernel 4.13.11

Signed-off-by: Sergey Matyukevich <geomatsi@gmail.com>
[Thomas: add entry to DEVELOPERS file.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
diff --git a/DEVELOPERS b/DEVELOPERS
index c44e8ae..ce32022 100644
--- a/DEVELOPERS
+++ b/DEVELOPERS
@@ -1511,8 +1511,10 @@
 F:	board/linksprite/pcduino
 F:	board/orangepi/orangepi-zero
 F:	board/orangepi/orangepi-one
+F:	board/orangepi/orangepi-pc-plus/
 F:	configs/linksprite_pcduino_defconfig
 F:	configs/orangepi_one_defconfig
+F:	configs/orangepi_pc_plus_defconfig
 F:	configs/orangepi_zero_defconfig
 F:	package/armbian-firmware/
 F:	package/xr819-xradio/