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/imx28_xea_defconfig b/configs/imx28_xea_defconfig
index 63d6101..4837209 100644
--- a/configs/imx28_xea_defconfig
+++ b/configs/imx28_xea_defconfig
@@ -48,6 +48,7 @@
 CONFIG_SYS_SPI_U_BOOT_OFFS=0x10000
 CONFIG_SPL_YMODEM_SUPPORT=y
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_MAXARGS=32
 CONFIG_CMD_SPL=y
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_GREPENV=y