RK3568-tftp更新设备树和内核&nfs挂载文件系统

1. 注意：需要设备树和内核按以下修改才能支持tftp和nfs。

1.1 修改设备树：

diff --git a/arch/arm64/boot/dts/rockchip/OK3568-C-linux.dts b/arch/arm64/boot/dts/rockchip/OK3568-C-linux.dts
index 178b4d831..34cb57ffd 100644
--- a/arch/arm64/boot/dts/rockchip/OK3568-C-linux.dts
+++ b/arch/arm64/boot/dts/rockchip/OK3568-C-linux.dts
@@ -2,6 +2,6 @@
 
 / {
        chosen: chosen {
-               bootargs = "earlycon=uart8250,mmio32,0xfe660000 console=ttyFIQ0 root=PARTUUID=614e0000-0000 rw rootwait";
+               bootargs = "earlycon=uart8250,mmio32,0xfe660000 console=ttyFIQ0 root=/dev/nfs rootfstype=ext4 rw rootwait";
        };
 };

1.2 修改默认配置文件：

diff --git a/arch/arm64/configs/OK3568-C-linux_defconfig b/arch/arm64/configs/OK3568-C-linux_defconfig
index 76ef7958a..7beb6e701 100644
--