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/cubieboard7_defconfig b/configs/cubieboard7_defconfig
index 677bff6..35fd580 100644
--- a/configs/cubieboard7_defconfig
+++ b/configs/cubieboard7_defconfig
@@ -13,6 +13,7 @@
 # CONFIG_DISPLAY_CPUINFO is not set
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SYS_PROMPT="U-Boot => "
+CONFIG_SYS_MAXARGS=64
 CONFIG_CMD_MMC=y
 CONFIG_MMC_OWL=y
 CONFIG_PHY_REALTEK=y