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/verdin-imx8mm_defconfig b/configs/verdin-imx8mm_defconfig
index 46d4dd7..1f77b30 100644
--- a/configs/verdin-imx8mm_defconfig
+++ b/configs/verdin-imx8mm_defconfig
@@ -39,6 +39,7 @@
 CONFIG_SPL_POWER=y
 CONFIG_SPL_WATCHDOG=y
 CONFIG_SYS_PROMPT="Verdin iMX8MM # "
+CONFIG_SYS_MAXARGS=64
 # CONFIG_BOOTM_NETBSD is not set
 CONFIG_CMD_ASKENV=y
 # CONFIG_CMD_EXPORTENV is not set