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/bcm7260_defconfig b/configs/bcm7260_defconfig
index 401a2d7..b8b744e 100644
--- a/configs/bcm7260_defconfig
+++ b/configs/bcm7260_defconfig
@@ -19,6 +19,7 @@
 CONFIG_BOARD_LATE_INIT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="U-Boot>"
+CONFIG_SYS_MAXARGS=32
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_GPT=y
 # CONFIG_RANDOM_UUID is not set