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/am65x_evm_r5_usbmsc_defconfig b/configs/am65x_evm_r5_usbmsc_defconfig
index e6147d1..3d8b6de 100644
--- a/configs/am65x_evm_r5_usbmsc_defconfig
+++ b/configs/am65x_evm_r5_usbmsc_defconfig
@@ -39,6 +39,7 @@
 CONFIG_SPL_USB_GADGET=y
 CONFIG_SPL_YMODEM_SUPPORT=y
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_MAXARGS=64
 CONFIG_CMD_BOOTZ=y
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_GPT=y