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/imx8mn_beacon_2g_defconfig b/configs/imx8mn_beacon_2g_defconfig
index 145f96d..593b803 100644
--- a/configs/imx8mn_beacon_2g_defconfig
+++ b/configs/imx8mn_beacon_2g_defconfig
@@ -40,6 +40,7 @@
 CONFIG_SPL_POWER=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="u-boot=> "
+CONFIG_SYS_MAXARGS=64
 # CONFIG_BOOTM_NETBSD is not set
 # CONFIG_CMD_EXPORTENV is not set
 # CONFIG_CMD_IMPORTENV is not set