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/xilinx_zynq_virt_defconfig b/configs/xilinx_zynq_virt_defconfig
index 61a748b..5e724f0 100644
--- a/configs/xilinx_zynq_virt_defconfig
+++ b/configs/xilinx_zynq_virt_defconfig
@@ -29,6 +29,8 @@
 CONFIG_USE_PREBOOT=y
 CONFIG_CLOCKS=y
 CONFIG_SPL_STACK_R=y
+CONFIG_SPL_FS_LOAD_PAYLOAD_NAME="u-boot.img"
+CONFIG_SPL_FS_LOAD_ARGS_NAME="system.dtb"
 CONFIG_SPL_FPGA=y
 CONFIG_SPL_OS_BOOT=y
 CONFIG_SPL_SPI_LOAD=y