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_hs_evm_usb_defconfig b/configs/dra7xx_hs_evm_usb_defconfig
index 5560a1b..12b92f3 100644
--- a/configs/dra7xx_hs_evm_usb_defconfig
+++ b/configs/dra7xx_hs_evm_usb_defconfig
@@ -41,6 +41,7 @@
 CONFIG_SPL_USB_GADGET=y
 CONFIG_SPL_DFU=y
 CONFIG_SPL_YMODEM_SUPPORT=y
+CONFIG_SYS_MAXARGS=64
 CONFIG_SYS_I2C_EEPROM_ADDR_LEN=2
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_SETEXPR is not set