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/configs/rock-pi-4-rk3399_defconfig b/configs/rock-pi-4-rk3399_defconfig
index 6dc6075..bca44be 100644
--- a/configs/rock-pi-4-rk3399_defconfig
+++ b/configs/rock-pi-4-rk3399_defconfig
@@ -8,7 +8,7 @@
 CONFIG_OF_LIBFDT_OVERLAY=y
 CONFIG_DM_RESET=y
 CONFIG_ROCKCHIP_RK3399=y
-CONFIG_TARGET_EVB_RK3399=y
+CONFIG_TARGET_ROCKPI4_RK3399=y
 CONFIG_DEBUG_UART_BASE=0xFF1A0000
 CONFIG_DEBUG_UART_CLOCK=24000000
 CONFIG_SYS_LOAD_ADDR=0x800800