The config option CONFIG_SILENT_CONSOLE can be used to quiet messages
on the console.  If the option has been enabled, the output can be
silenced by setting the environment variable "silent".

- CONFIG_SILENT_CONSOLE_UPDATE_ON_SET
	When the "silent" variable is changed with env set, the change
	will take effect immediately.

- CONFIG_SILENT_CONSOLE_UPDATE_ON_RELOC
	Some environments are not available until relocation (e.g. NAND)
	so this will make the value in the flash env take effect at
	relocation.

The following actions are taken if "silent" is set at boot time:

 - Until the console devices have been initialized, output has to be
   suppressed by testing for the flag "GD_FLG_SILENT" in "gd->flags".

 - When the console devices have been initialized, "stdout" and
   "stderr" are set to "nulldev", so subsequent messages are
   suppressed automatically. Make sure to enable "nulldev" by
   enabling CONFIG_SYS_DEVICE_NULLDEV in your board defconfig file.

 - When booting a linux kernel, the "bootargs" are fixed up so that
   the argument "console=" will be in the command line, no matter how
   it was set in "bootargs" before. If you don't want the linux command
   line to be affected, define CONFIG_SILENT_U_BOOT_ONLY in your board
   config file as well, and this part of the feature will be disabled.
