board: rockchip: add Powkiddy X55

The Powkiddy X55 is a Rockchip RK3566 based handheld gaming device.
UART, ADC, eMMC, and SDMMC are tested to work in U-Boot and this
successfully boots mainline Linux.

Kernel commit:
e99adc97e21a ("arm64: dts: rockchip: Add Powkiddy X55")

Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/arch/arm/mach-rockchip/rk3568/Kconfig b/arch/arm/mach-rockchip/rk3568/Kconfig
index af537d9..014ebf9 100644
--- a/arch/arm/mach-rockchip/rk3568/Kconfig
+++ b/arch/arm/mach-rockchip/rk3568/Kconfig
@@ -22,6 +22,11 @@
 	help
 	  Hardkernel ODROID-M1 single board computer with a RK3568B2 SoC.
 
+config TARGET_POWKIDDY_X55_RK3566
+	bool "Powkiddy X55"
+	help
+	  Powkiddy X55 handheld gaming console with an RK3566 SoC.
+
 config TARGET_QUARTZ64_RK3566
 	bool "Pine64 Quartz64"
 	help
@@ -48,5 +53,6 @@
 source "board/anbernic/rgxx3_rk3566/Kconfig"
 source "board/hardkernel/odroid_m1/Kconfig"
 source "board/pine64/quartz64_rk3566/Kconfig"
+source "board/powkiddy/x55/Kconfig"
 
 endif