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/poleg_evb_defconfig b/configs/poleg_evb_defconfig
index 94bb34a..6d1b2bd 100644
--- a/configs/poleg_evb_defconfig
+++ b/configs/poleg_evb_defconfig
@@ -16,6 +16,7 @@
 CONFIG_USE_BOOTCOMMAND=y
 CONFIG_BOOTCOMMAND="run common_bootargs; run romboot"
 CONFIG_SYS_PROMPT="U-Boot>"
+CONFIG_SYS_MAXARGS=32
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_SPI=y
 CONFIG_CMD_CACHE=y