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/am335x_guardian_defconfig b/configs/am335x_guardian_defconfig
index 7925e10..738d4bb 100644
--- a/configs/am335x_guardian_defconfig
+++ b/configs/am335x_guardian_defconfig
@@ -43,6 +43,7 @@
 CONFIG_SPL_POWER=y
 CONFIG_SPL_USB_GADGET=y
 CONFIG_SPL_USB_ETHER=y
+CONFIG_SYS_MAXARGS=64
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_MEMINFO=y
 CONFIG_CMD_MEMTEST=y