Convert CONFIG_SYS_STDIO_DEREGISTER to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_STDIO_DEREGISTER

This option should never be enabled in SPL, so use
CONFIG_IS_ENABLED(SYS_STDIO_DEREGISTER) when checking the option.

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: Re-sync]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/nyan-big_defconfig b/configs/nyan-big_defconfig
index 2a1d318..ae3f84c 100644
--- a/configs/nyan-big_defconfig
+++ b/configs/nyan-big_defconfig
@@ -6,6 +6,7 @@
 CONFIG_FIT=y
 CONFIG_FIT_BEST_MATCH=y
 CONFIG_OF_SYSTEM_SETUP=y
+CONFIG_SYS_STDIO_DEREGISTER=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="Tegra124 (Nyan-big) # "
 CONFIG_CMD_BOOTZ=y