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/vexpress_aemv8a_semi_defconfig b/configs/vexpress_aemv8a_semi_defconfig
index 1a4cbc1..7e4a5cc 100644
--- a/configs/vexpress_aemv8a_semi_defconfig
+++ b/configs/vexpress_aemv8a_semi_defconfig
@@ -14,6 +14,7 @@
 CONFIG_BOOTARGS="console=ttyAMA0 earlycon=pl011,0x1c090000 debug user_debug=31 loglevel=9"
 # CONFIG_DISPLAY_CPUINFO is not set
 CONFIG_SYS_PROMPT="VExpress64# "
+CONFIG_SYS_MAXARGS=64
 CONFIG_CMD_ABOOTIMG=y
 CONFIG_CMD_MEMTEST=y
 CONFIG_CMD_ARMFLASH=y