Convert CONFIG_SPL_FS_LOAD_PAYLOAD_NAME et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SPL_FS_LOAD_ARGS_NAME
   CONFIG_SPL_FS_LOAD_KERNEL_NAME
   CONFIG_SPL_FS_LOAD_PAYLOAD_NAME

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/mx6cuboxi_defconfig b/configs/mx6cuboxi_defconfig
index b5bff66..41122ad 100644
--- a/configs/mx6cuboxi_defconfig
+++ b/configs/mx6cuboxi_defconfig
@@ -27,6 +27,7 @@
 CONFIG_PREBOOT="if hdmidet; then usb start; setenv stdin  serial,usbkbd; setenv stdout serial,vidconsole; setenv stderr serial,vidconsole; else setenv stdin  serial; setenv stdout serial; setenv stderr serial; fi;"
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SPL_FS_EXT4=y
+CONFIG_SPL_FS_LOAD_PAYLOAD_NAME="u-boot-dtb.img"
 CONFIG_SPL_I2C=y
 CONFIG_SPL_WATCHDOG=y
 CONFIG_SYS_MAXARGS=32