Convert CONFIG_SYS_MAXARGS to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_MAXARGS

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/nyan-big_defconfig b/configs/nyan-big_defconfig
index f82bace..0c906fc 100644
--- a/configs/nyan-big_defconfig
+++ b/configs/nyan-big_defconfig
@@ -24,6 +24,7 @@
 CONFIG_SYS_STDIO_DEREGISTER=y
 CONFIG_DISPLAY_BOARDINFO_LATE=y
 CONFIG_SYS_PROMPT="Tegra124 (Nyan-big) # "
+CONFIG_SYS_MAXARGS=64
 # CONFIG_CMD_IMI is not set
 CONFIG_CMD_DFU=y
 CONFIG_CMD_GPIO=y