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_boneblack_vboot_defconfig b/configs/am335x_boneblack_vboot_defconfig
index dc4693d..53ebc6d 100644
--- a/configs/am335x_boneblack_vboot_defconfig
+++ b/configs/am335x_boneblack_vboot_defconfig
@@ -29,6 +29,7 @@
 CONFIG_SYS_MMCSD_RAW_MODE_KERNEL_SECTOR=0x1700
 CONFIG_SPL_USB_GADGET=y
 CONFIG_SPL_USB_ETHER=y
+CONFIG_SYS_MAXARGS=64
 CONFIG_CMD_SPL=y
 CONFIG_SYS_I2C_EEPROM_ADDR_LEN=2
 # CONFIG_CMD_FLASH is not set