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/mt7622_rfb_defconfig b/configs/mt7622_rfb_defconfig
index 90e8d77..1f12cfd 100644
--- a/configs/mt7622_rfb_defconfig
+++ b/configs/mt7622_rfb_defconfig
@@ -14,6 +14,7 @@
 CONFIG_LOGLEVEL=7
 CONFIG_LOG=y
 CONFIG_SYS_PROMPT="MT7622> "
+CONFIG_SYS_MAXARGS=8
 CONFIG_CMD_BOOTMENU=y
 CONFIG_CMD_MMC=y
 CONFIG_CMD_PCI=y