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/am335x_hs_evm_uart_defconfig b/configs/am335x_hs_evm_uart_defconfig
index 48e72f8..120f3ad 100644
--- a/configs/am335x_hs_evm_uart_defconfig
+++ b/configs/am335x_hs_evm_uart_defconfig
@@ -28,6 +28,7 @@
 CONFIG_SPL_NAND_DRIVERS=y
 CONFIG_SPL_NAND_ECC=y
 CONFIG_SPL_NAND_BASE=y
+CONFIG_SYS_MAXARGS=64
 CONFIG_SYS_I2C_EEPROM_ADDR_LEN=2
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_NAND=y