spi: add support for MediaTek spi-mem controller

This patch adds support for spi-mem controller found on newer MediaTek SoCs
This controller supports Single/Dual/Quad SPI mode.

Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Daniel Golle <daniel@makrotopia.org>
diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index ac91d82..07e50e2 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -286,6 +286,14 @@
 	  used to access SPI memory devices like SPI-NOR or SPI-NAND on
 	  platforms embedding this IP core, like MT7622/M7629.
 
+config MTK_SPIM
+	bool "Mediatek SPI-MEM master controller driver"
+	depends on SPI_MEM
+	help
+	  Enable MediaTek SPI-MEM master controller driver. This driver mainly
+	  supports SPI flashes. You can use single, dual or quad mode
+	  transmission on this controller.
+
 config MVEBU_A3700_SPI
 	bool "Marvell Armada 3700 SPI driver"
 	select CLK_ARMADA_3720