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-imx8mp_defconfig b/configs/verdin-imx8mp_defconfig
index 4b7cf74..c09d561 100644
--- a/configs/verdin-imx8mp_defconfig
+++ b/configs/verdin-imx8mp_defconfig
@@ -49,6 +49,7 @@
 CONFIG_SPL_POWER=y
 CONFIG_SPL_WATCHDOG=y
 CONFIG_SYS_PROMPT="Verdin iMX8MP # "
+CONFIG_SYS_MAXARGS=64
 # CONFIG_BOOTM_NETBSD is not set
 CONFIG_CMD_ASKENV=y
 # CONFIG_CMD_EXPORTENV is not set