board: rockchip: Add a common ROCK Pi 4 target

Move ROCK Pi 4 specific board code from the shared evb_rk3399 target
into its own board target and update related defconfigs to use the new
TARGET_ROCKPI4_RK3399 option.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Christopher Obbard <chris.obbard@collabora.com>
Reviewed-by: Peter Robinson <pbrobinson@gmail.com>
diff --git a/arch/arm/mach-rockchip/rk3399/Kconfig b/arch/arm/mach-rockchip/rk3399/Kconfig
index 3890429..04a84e2 100644
--- a/arch/arm/mach-rockchip/rk3399/Kconfig
+++ b/arch/arm/mach-rockchip/rk3399/Kconfig
@@ -89,6 +89,11 @@
 	   * 2x USB 3.0 type A, 2x USB 2.0 type A (host mode only),
 	     1x USB 3.0 type C OTG
 
+config TARGET_ROCKPI4_RK3399
+	bool "Radxa ROCK Pi 4 board"
+	help
+	  Support for ROCK Pi 4 board family by Radxa.
+
 config TARGET_ROCKPRO64_RK3399
 	bool "Pine64 Rockpro64 board"
 	help
@@ -177,6 +182,7 @@
 source "board/pine64/pinebook-pro-rk3399/Kconfig"
 source "board/pine64/pinephone-pro-rk3399/Kconfig"
 source "board/pine64/rockpro64_rk3399/Kconfig"
+source "board/radxa/rockpi4-rk3399/Kconfig"
 source "board/rockchip/evb_rk3399/Kconfig"
 source "board/theobroma-systems/puma_rk3399/Kconfig"
 source "board/vamrs/rock960_rk3399/Kconfig"