riscv: ax25-ae350: add SPL configuration

This patch provides four configurations which can support U-Boot SPL
to boot from RAM or FLASH and then boot FIT image including OpenSBI
FW_DYNAMIC firmware and U-Boot proper images from RAM or MMC boot devices.

With ae350_rv[32|64]_spl_defconfigs:

U-Boot SPL will be loaded by gdb or FSBL and runs in RAM in machine mode
and then load FIT image from RAM device on AE350.

With ae350_rv[32|64]_spl_xip_defconfigs:

U-Boot SPL can be burned into SPI flash and run in flash in machine mode
and then load FIT image from SPI flash or MMC device on AE350.

Signed-off-by: Rick Chen <rick@andestech.com>
Cc: KC Lin <kclin@andestech.com>
Cc: Alan Kao <alankao@andestech.com>
diff --git a/configs/ae350_rv32_spl_defconfig b/configs/ae350_rv32_spl_defconfig
new file mode 100644
index 0000000..8bd6a26
--- /dev/null
+++ b/configs/ae350_rv32_spl_defconfig
@@ -0,0 +1,38 @@
+CONFIG_RISCV=y
+CONFIG_SPL=y
+CONFIG_RISCV_SMODE=y
+CONFIG_SYS_TEXT_BASE=0x01200000
+CONFIG_NR_DRAM_BANKS=2
+CONFIG_TARGET_AX25_AE350=y
+CONFIG_DISTRO_DEFAULTS=y
+CONFIG_FIT=y
+CONFIG_BOOTDELAY=3
+CONFIG_BOARD_EARLY_INIT_F=y
+CONFIG_SYS_PROMPT="RISC-V # "
+CONFIG_CMD_IMLS=y
+CONFIG_CMD_MMC=y
+CONFIG_CMD_SF=y
+CONFIG_CMD_SF_TEST=y
+# CONFIG_CMD_SETEXPR is not set
+CONFIG_BOOTP_PREFER_SERVERIP=y
+CONFIG_CMD_CACHE=y
+CONFIG_OF_PRIOR_STAGE=y
+CONFIG_ENV_IS_IN_SPI_FLASH=y
+CONFIG_ENV_SECT_SIZE=0x1000
+CONFIG_NET_RANDOM_ETHADDR=y
+CONFIG_MMC=y
+CONFIG_FTSDC010=y
+CONFIG_FTSDC010_SDIO=y
+CONFIG_MTD_NOR_FLASH=y
+CONFIG_FLASH_CFI_DRIVER=y
+CONFIG_CFI_FLASH=y
+CONFIG_SYS_FLASH_USE_BUFFER_WRITE=y
+CONFIG_SYS_FLASH_CFI=y
+CONFIG_SPI_FLASH=y
+CONFIG_SF_DEFAULT_MODE=0x0
+CONFIG_SPI_FLASH_MACRONIX=y
+CONFIG_FTMAC100=y
+CONFIG_BAUDRATE=38400
+CONFIG_SYS_NS16550=y
+CONFIG_SPI=y
+CONFIG_ATCSPI200_SPI=y