board: mediatek: add MT7981 reference boards

This patch adds general board files based on MT7981 SoCs.

MT7981 uses one mmc controller for booting from both SD and eMMC, and the
pins of mmc controller are also shared with spi controller.
So three configs are need for these boot types:

1. mt7981_rfb_defconfig - SPI-NOR and SPI-NAND
2. mt7981_emmc_rfb_defconfig - eMMC only
3. mt7981_sd_rfb_defconfig - SD only

Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/mt7981_rfb_defconfig b/configs/mt7981_rfb_defconfig
new file mode 100644
index 0000000..88299e3
--- /dev/null
+++ b/configs/mt7981_rfb_defconfig
@@ -0,0 +1,69 @@
+CONFIG_ARM=y
+CONFIG_POSITION_INDEPENDENT=y
+CONFIG_ARCH_MEDIATEK=y
+CONFIG_SYS_TEXT_BASE=0x41e00000
+CONFIG_SYS_MALLOC_F_LEN=0x4000
+CONFIG_NR_DRAM_BANKS=1
+CONFIG_DEFAULT_DEVICE_TREE="mt7981-rfb"
+CONFIG_TARGET_MT7981=y
+CONFIG_DEBUG_UART_BASE=0x11002000
+CONFIG_DEBUG_UART_CLOCK=40000000
+CONFIG_SYS_LOAD_ADDR=0x46000000
+CONFIG_DEBUG_UART=y
+# CONFIG_AUTOBOOT is not set
+CONFIG_DEFAULT_FDT_FILE="mt7981-rfb"
+CONFIG_LOGLEVEL=7
+CONFIG_LOG=y
+CONFIG_SYS_PROMPT="MT7981> "
+CONFIG_SYS_CBSIZE=512
+CONFIG_SYS_PBSIZE=1049
+# CONFIG_BOOTM_NETBSD is not set
+# CONFIG_BOOTM_PLAN9 is not set
+# CONFIG_BOOTM_RTEMS is not set
+# CONFIG_BOOTM_VXWORKS is not set
+# CONFIG_CMD_ELF is not set
+# CONFIG_CMD_UNLZ4 is not set
+# CONFIG_CMD_UNZIP is not set
+CONFIG_CMD_GPIO=y
+CONFIG_CMD_MTD=y
+CONFIG_CMD_SF_TEST=y
+CONFIG_CMD_PING=y
+CONFIG_CMD_SMC=y
+CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
+CONFIG_NET_RANDOM_ETHADDR=y
+CONFIG_REGMAP=y
+CONFIG_SYSCON=y
+CONFIG_BLK=y
+CONFIG_HAVE_BLOCK_DEVICE=y
+CONFIG_CLK=y
+# CONFIG_MMC is not set
+CONFIG_MTD=y
+CONFIG_DM_MTD=y
+CONFIG_MTD_SPI_NAND=y
+CONFIG_DM_SPI_FLASH=y
+CONFIG_SPI_FLASH_SFDP_SUPPORT=y
+CONFIG_SPI_FLASH_EON=y
+CONFIG_SPI_FLASH_GIGADEVICE=y
+CONFIG_SPI_FLASH_ISSI=y
+CONFIG_SPI_FLASH_MACRONIX=y
+CONFIG_SPI_FLASH_SPANSION=y
+CONFIG_SPI_FLASH_STMICRO=y
+CONFIG_SPI_FLASH_WINBOND=y
+CONFIG_SPI_FLASH_XMC=y
+CONFIG_SPI_FLASH_XTX=y
+CONFIG_SPI_FLASH_MTD=y
+CONFIG_PHY_FIXED=y
+CONFIG_DM_ETH=y
+CONFIG_MEDIATEK_ETH=y
+CONFIG_PINCTRL=y
+CONFIG_PINCONF=y
+CONFIG_PINCTRL_MT7981=y
+CONFIG_POWER_DOMAIN=y
+CONFIG_MTK_POWER_DOMAIN=y
+CONFIG_DM_SERIAL=y
+CONFIG_MTK_SERIAL=y
+CONFIG_SPI=y
+CONFIG_DM_SPI=y
+CONFIG_MTK_SPIM=y
+CONFIG_HEXDUMP=y
+# CONFIG_EFI_LOADER is not set