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/xenguest_arm64_defconfig b/configs/xenguest_arm64_defconfig
index 11fca09..93e0b7f 100644
--- a/configs/xenguest_arm64_defconfig
+++ b/configs/xenguest_arm64_defconfig
@@ -11,6 +11,7 @@
 CONFIG_OF_SYSTEM_SETUP=y
 CONFIG_BOOTDELAY=10
 CONFIG_SYS_PROMPT="xenguest# "
+CONFIG_SYS_MAXARGS=64
 # CONFIG_CMD_BDI is not set
 # CONFIG_CMD_BOOTD is not set
 # CONFIG_CMD_ELF is not set