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/nanopi-k2_defconfig b/configs/nanopi-k2_defconfig
index f7d8f78..bd715b3 100644
--- a/configs/nanopi-k2_defconfig
+++ b/configs/nanopi-k2_defconfig
@@ -14,6 +14,7 @@
 CONFIG_OF_BOARD_SETUP=y
 # CONFIG_DISPLAY_CPUINFO is not set
 CONFIG_MISC_INIT_R=y
+CONFIG_SYS_MAXARGS=32
 # CONFIG_CMD_BDI is not set
 # CONFIG_CMD_IMI is not set
 CONFIG_CMD_GPIO=y