mips: mtmips: add support for mt7628-rfb

This patch adds support for mt7628 reference board. SPL_DM and DT are not
enabled for SPL to save about 17KiB for u-boot-spl.bin.

Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/arch/mips/mach-mtmips/Kconfig b/arch/mips/mach-mtmips/Kconfig
index 5a5f2e3..60cc0f8 100644
--- a/arch/mips/mach-mtmips/Kconfig
+++ b/arch/mips/mach-mtmips/Kconfig
@@ -79,6 +79,14 @@
 	  ethernet ports, 1 USB port, 1 UART, GPIO buttons and LEDs, and
 	  a MT7688 (PCIe).
 
+config BOARD_MT7628_RFB
+	bool "MediaTek MT7628 RFB"
+	depends on SOC_MT7628
+	help
+	  The reference design of MT7628. The board has 128 MiB DDR2, 8 MiB
+	  SPI-NOR flash, 1 built-in switch with 5 ports, 1 UART, 1 USB host,
+	  1 SDXC, 1 PCIe socket and JTAG pins.
+
 endchoice
 
 config SPL_UART2_SPIS_PINMUX
@@ -90,6 +98,7 @@
 	  (shared with SPIS) rather than the usual GPIO 20/21.
 
 source "board/gardena/smart-gateway-mt7688/Kconfig"
+source "board/mediatek/mt7628/Kconfig"
 source "board/seeed/linkit-smart-7688/Kconfig"
 
 endmenu