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/dra7xx_evm_defconfig b/configs/dra7xx_evm_defconfig
index dcb7b3f..f04a2fb 100644
--- a/configs/dra7xx_evm_defconfig
+++ b/configs/dra7xx_evm_defconfig
@@ -28,6 +28,7 @@
 # CONFIG_MISC_INIT_R is not set
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 CONFIG_SPL_DMA=y
+CONFIG_SPL_FS_LOAD_PAYLOAD_NAME="u-boot.img"
 CONFIG_SPL_NAND_DRIVERS=y
 CONFIG_SPL_NAND_ECC=y
 CONFIG_SPL_NAND_BASE=y