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/microblaze-generic_defconfig b/configs/microblaze-generic_defconfig
index 3142b46..6823d41 100644
--- a/configs/microblaze-generic_defconfig
+++ b/configs/microblaze-generic_defconfig
@@ -30,6 +30,7 @@
 CONFIG_SPL_OS_BOOT=y
 CONFIG_SYS_OS_BASE=0x2c060000
 CONFIG_SYS_PROMPT="U-Boot-mONStR> "
+CONFIG_SYS_MAXARGS=15
 CONFIG_CMD_IMLS=y
 CONFIG_CMD_SPL=y
 CONFIG_CMD_ASKENV=y