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_evm_spiboot_defconfig b/configs/am335x_evm_spiboot_defconfig
index f1b9d6c..3f3a81a 100644
--- a/configs/am335x_evm_spiboot_defconfig
+++ b/configs/am335x_evm_spiboot_defconfig
@@ -26,6 +26,7 @@
 CONFIG_SPL_DM_SPI_FLASH=y
 CONFIG_SPL_SPI_LOAD=y
 CONFIG_SYS_SPI_U_BOOT_OFFS=0x20000
+CONFIG_SYS_MAXARGS=64
 CONFIG_CMD_SPL=y
 CONFIG_SYS_I2C_EEPROM_ADDR_LEN=2
 # CONFIG_CMD_FLASH is not set