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/omap3_beagle_defconfig b/configs/omap3_beagle_defconfig
index 4767c0b..5c3c846 100644
--- a/configs/omap3_beagle_defconfig
+++ b/configs/omap3_beagle_defconfig
@@ -22,6 +22,7 @@
 CONFIG_SPL_NAND_SIMPLE=y
 CONFIG_SPL_NAND_BASE=y
 CONFIG_SYS_PROMPT="BeagleBoard # "
+CONFIG_SYS_MAXARGS=64
 CONFIG_CMD_SPL=y
 CONFIG_CMD_SPL_NAND_OFS=0x280000
 CONFIG_CMD_SPL_WRITE_SIZE=0x20000