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/omap5_uevm_defconfig b/configs/omap5_uevm_defconfig
index 4c66a4c..748b012 100644
--- a/configs/omap5_uevm_defconfig
+++ b/configs/omap5_uevm_defconfig
@@ -18,6 +18,7 @@
 CONFIG_SPL_OS_BOOT=y
 CONFIG_SPL_FALCON_BOOT_MMCSD=y
 CONFIG_SYS_MMCSD_RAW_MODE_KERNEL_SECTOR=0x1700
+CONFIG_SYS_MAXARGS=64
 CONFIG_CMD_SPL=y
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_DFU=y