[U-Boot] Disable tftp and access

[Nable]

Hi!

I haven't tested this approach, but you can define the following variables
in your board config (see include/configs/mimc200.h for example):
#define CONFIG_SILENT_CONSOLE       /* enable silent startup */
#define CONFIG_DISABLE_CONSOLE      /* disable console */
#define CONFIG_SYS_DEVICE_NULLDEV   /* include nulldev device */

Then you can set "stdin=nulldev\0" in your environment. I hope it helps.

I should also mention that if you are going to sell devices and want to
completely disable access to the firmware/software, then you should also
somehow disable debug ports (such as JTAG).