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/imx8mm_beacon_defconfig b/configs/imx8mm_beacon_defconfig
index 9cd8ac9..7e3b95ea 100644
--- a/configs/imx8mm_beacon_defconfig
+++ b/configs/imx8mm_beacon_defconfig
@@ -33,6 +33,7 @@
 CONFIG_SPL_WATCHDOG=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="u-boot=> "
+CONFIG_SYS_MAXARGS=64
 # CONFIG_CMD_EXPORTENV is not set
 # CONFIG_CMD_IMPORTENV is not set
 # CONFIG_CMD_CRC32 is not set