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/p2371-2180_defconfig b/configs/p2371-2180_defconfig
index 5977325..5fbcb7d 100644
--- a/configs/p2371-2180_defconfig
+++ b/configs/p2371-2180_defconfig
@@ -16,6 +16,7 @@
 CONFIG_CONSOLE_MUX=y
 CONFIG_SYS_STDIO_DEREGISTER=y
 CONFIG_SYS_PROMPT="Tegra210 (P2371-2180) # "
+CONFIG_SYS_MAXARGS=64
 # CONFIG_CMD_IMI is not set
 CONFIG_CMD_DFU=y
 CONFIG_CMD_GPIO=y