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/ti816x_evm_defconfig b/configs/ti816x_evm_defconfig
index d328ea1..85d7d26 100644
--- a/configs/ti816x_evm_defconfig
+++ b/configs/ti816x_evm_defconfig
@@ -33,6 +33,7 @@
 CONFIG_SPL_NAND_DRIVERS=y
 CONFIG_SPL_NAND_ECC=y
 CONFIG_SPL_NAND_BASE=y
+CONFIG_SYS_MAXARGS=64
 CONFIG_CMD_ASKENV=y
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_GPIO=y