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/imx8qxp_mek_defconfig b/configs/imx8qxp_mek_defconfig
index 43f42f7..23f9e3a 100644
--- a/configs/imx8qxp_mek_defconfig
+++ b/configs/imx8qxp_mek_defconfig
@@ -34,6 +34,7 @@
 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR=0x800
 CONFIG_SPL_POWER_DOMAIN=y
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_MAXARGS=64
 CONFIG_CMD_CPU=y
 # CONFIG_BOOTM_NETBSD is not set
 # CONFIG_CMD_EXPORTENV is not set