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/dra7xx_evm_defconfig b/configs/dra7xx_evm_defconfig
index e972d3b..dcb7b3f 100644
--- a/configs/dra7xx_evm_defconfig
+++ b/configs/dra7xx_evm_defconfig
@@ -40,6 +40,7 @@
 CONFIG_SYS_SPI_U_BOOT_OFFS=0x40000
 CONFIG_SPL_USB_GADGET=y
 CONFIG_SPL_DFU=y
+CONFIG_SYS_MAXARGS=64
 CONFIG_CMD_SPL=y
 CONFIG_SYS_I2C_EEPROM_ADDR_LEN=2
 # CONFIG_CMD_FLASH is not set