mips: mtmips: move mt7628 related Kconfig into mt7628 subdirectory

This patch is a preparation for add a new soc fot mtmips.

Move all mt7628 related Kconfig (boards and UART selection) into mt7628
subdirectory and make sure the top directory of mtmips contains only
selection for SoCs.

Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/arch/mips/mach-mtmips/Kconfig b/arch/mips/mach-mtmips/Kconfig
index 737de2c..7c07430 100644
--- a/arch/mips/mach-mtmips/Kconfig
+++ b/arch/mips/mach-mtmips/Kconfig
@@ -58,57 +58,6 @@
 
 endchoice
 
-choice
-	prompt "Board select"
-
-config BOARD_GARDENA_SMART_GATEWAY_MT7688
-	bool "GARDENA smart Gateway"
-	depends on SOC_MT7628
-	select BOARD_LATE_INIT
-	help
-	  GARDENA smart Gateway boards have a MT7688 SoC with 128 MiB of RAM
-	  and 8 MiB of flash (SPI NOR) and additional SPI NAND storage.
-
-config BOARD_LINKIT_SMART_7688
-	bool "LinkIt Smart 7688"
-	depends on SOC_MT7628
-	help
-	  Seeed LinkIt Smart 7688 boards have a MT7688 SoC with 128 MiB of RAM
-	  and 32 MiB of flash (SPI).
-	  Between its different peripherals there's an integrated switch with 4
-	  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.
-
-config BOARD_VOCORE2
-	bool "VoCore2"
-	depends on SOC_MT7628
-	select SPL_SERIAL_SUPPORT
-	select SPL_UART2_SPIS_PINMUX
-	help
-	  VoCore VoCore2 board has a MT7628 SoC with 128 MiB of RAM
-	  and 16 MiB of flash (SPI).
-
-endchoice
-
-config SPL_UART2_SPIS_PINMUX
-	bool "Use alternative pinmux for UART2 in SPL stage"
-	depends on SPL_SERIAL_SUPPORT
-	default n
-	help
-	  Select this if the UART2 of your board is connected to GPIO 16/17
-	  (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"
-source "board/vocore/vocore2/Kconfig"
+source "arch/mips/mach-mtmips/mt7628/Kconfig"
 
 endmenu