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/mx6sabresd_defconfig b/configs/mx6sabresd_defconfig
index 674384c..9b3d594 100644
--- a/configs/mx6sabresd_defconfig
+++ b/configs/mx6sabresd_defconfig
@@ -38,6 +38,7 @@
 CONFIG_SPL_USB_SDP_SUPPORT=y
 CONFIG_SPL_WATCHDOG=y
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_MAXARGS=32
 CONFIG_CMD_BOOTZ=y
 CONFIG_CMD_SPL=y
 CONFIG_CMD_SPL_WRITE_SIZE=0x20000