arm: mvebu: add DB-88F6820-AMC board

This board is a plug in card for Marvell's switch system development
kits. Form-factor aside it is similar to the DB-88F6820-GP with the
following differences.
- TCLK is 200MHz
- SPI1 is used
- No SATA
- No MMC
- NAND flash

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Stefan Roese <sr@denx.de>

configs/db-88f6820-amc_defconfig

@@ -0,0 +1,43 @@
+CONFIG_ARM=y
+CONFIG_ARCH_MVEBU=y
+CONFIG_SPL_LIBCOMMON_SUPPORT=y
+CONFIG_SPL_LIBGENERIC_SUPPORT=y
+CONFIG_TARGET_DB_88F6820_AMC=y
+CONFIG_SPL_I2C_SUPPORT=y
+CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SPI_FLASH_SUPPORT=y
+CONFIG_SPL_SPI_SUPPORT=y
+CONFIG_DEFAULT_DEVICE_TREE="armada-385-amc"
+CONFIG_BOOTDELAY=3
+CONFIG_SPL=y
+# CONFIG_CMD_IMLS is not set
+# CONFIG_CMD_FLASH is not set
+CONFIG_CMD_SF=y
+CONFIG_CMD_SPI=y
+CONFIG_CMD_I2C=y
+CONFIG_CMD_USB=y
+# CONFIG_CMD_SETEXPR is not set
+CONFIG_CMD_TFTPPUT=y
+CONFIG_CMD_DHCP=y
+CONFIG_CMD_MII=y
+CONFIG_CMD_PING=y
+CONFIG_CMD_CACHE=y
+CONFIG_CMD_TIME=y
+CONFIG_CMD_EXT2=y
+CONFIG_CMD_EXT4=y
+CONFIG_CMD_FAT=y
+CONFIG_CMD_FS_GENERIC=y
+CONFIG_SPL_OF_TRANSLATE=y
+CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_BAR=y
+CONFIG_SPI_FLASH_MACRONIX=y
+CONFIG_SPI_FLASH_STMICRO=y
+CONFIG_DEBUG_UART=y
+CONFIG_DEBUG_UART_BASE=0xd0012000
+CONFIG_DEBUG_UART_CLOCK=200000000
+CONFIG_DEBUG_UART_SHIFT=2
+CONFIG_SYS_NS16550=y
+CONFIG_USB=y
+CONFIG_DM_USB=y
+CONFIG_USB_EHCI_HCD=y
+CONFIG_USB_STORAGE=y