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/j721s2_evm_a72_defconfig b/configs/j721s2_evm_a72_defconfig
index 6bb2e6a..90b9411 100644
--- a/configs/j721s2_evm_a72_defconfig
+++ b/configs/j721s2_evm_a72_defconfig
@@ -39,6 +39,7 @@
 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR=0x1400
 CONFIG_SPL_DMA=y
 CONFIG_SPL_ENV_SUPPORT=y
+CONFIG_SPL_FS_LOAD_PAYLOAD_NAME="u-boot.img"
 CONFIG_SPL_I2C=y
 CONFIG_SPL_DM_MAILBOX=y
 CONFIG_SPL_MTD_SUPPORT=y