Add support for MT7622 reference board

This adds a general board file based on MT7622 SoCs from MediaTek.
This commit is adding the basic boot support for the MT7622 rfb.

Tested-by: Frank Wunderlich <frank-w@public-files.de>
diff --git a/configs/mt7622_rfb_defconfig b/configs/mt7622_rfb_defconfig
new file mode 100644
index 0000000..e1917e7
--- /dev/null
+++ b/configs/mt7622_rfb_defconfig
@@ -0,0 +1,55 @@
+CONFIG_ARM=y
+CONFIG_POSITION_INDEPENDENT=y
+CONFIG_ARCH_MEDIATEK=y
+CONFIG_TARGET_MT7622=y
+CONFIG_SYS_TEXT_BASE=0x41e00000
+CONFIG_SYS_MALLOC_F_LEN=0x4000
+CONFIG_NR_DRAM_BANKS=1
+CONFIG_SMBIOS_PRODUCT_NAME=""
+CONFIG_FIT=y
+CONFIG_LOGLEVEL=7
+CONFIG_LOG=y
+CONFIG_LOG_MAX_LEVEL=6
+CONFIG_DEFAULT_FDT_FILE="mt7622-rfb"
+CONFIG_SYS_PROMPT="MT7622> "
+CONFIG_CMD_BOOTMENU=y
+CONFIG_CMD_MMC=y
+CONFIG_CMD_SF_TEST=y
+CONFIG_CMD_SMC=y
+CONFIG_DEFAULT_DEVICE_TREE="mt7622-rfb"
+CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
+CONFIG_REGMAP=y
+CONFIG_SYSCON=y
+CONFIG_CLK=y
+CONFIG_DM_GPIO=y
+CONFIG_DM_MMC=y
+CONFIG_MMC_HS200_SUPPORT=y
+CONFIG_MMC_MTK=y
+CONFIG_DM_SPI_FLASH=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_DM_ETH=y
+CONFIG_PINCTRL=y
+CONFIG_PINCONF=y
+CONFIG_PINCTRL_MT7622=y
+CONFIG_POWER_DOMAIN=y
+CONFIG_MTK_POWER_DOMAIN=y
+CONFIG_RAM=y
+CONFIG_DM_RESET=y
+CONFIG_DM_SERIAL=y
+CONFIG_MTK_SERIAL=y
+CONFIG_SPI=y
+CONFIG_DM_SPI=y
+CONFIG_MTK_SNFI_SPI=y
+CONFIG_SYSRESET_WATCHDOG=y
+CONFIG_TIMER=y
+CONFIG_MTK_TIMER=y
+CONFIG_WDT_MTK=y
+CONFIG_LZ4=y
+CONFIG_LZO=y
+CONFIG_HEXDUMP=y