nand: raw: add support for MediaTek MT7621 SoC

This patch adds NAND flash controller driver for MediaTek MT7621 SoC.
The NAND flash controller of MT7621 supports only SLC NAND flashes.
It supports 4~12 bits correction with maximum 4KB page size.

diff --git a/drivers/mtd/nand/raw/Kconfig b/drivers/mtd/nand/raw/Kconfig
index 190300f..ce67d1a 100644
--- a/drivers/mtd/nand/raw/Kconfig
+++ b/drivers/mtd/nand/raw/Kconfig
@@ -526,12 +526,25 @@
 	help
 	  Enables support for NAND Flash chips on Tegra SoCs platforms.
 
+config NAND_MT7621
+	bool "Support for MediaTek MT7621 NAND flash controller"
+	depends on SOC_MT7621
+	select SYS_NAND_SELF_INIT
+	select SPL_SYS_NAND_SELF_INIT
+	imply CMD_NAND
+	help
+	  This enables NAND driver for the NAND flash controller on MediaTek
+	  MT7621 platform.
+	  The controller supports 4~12 bits correction per 512 bytes with a
+	  maximum 4KB page size.
+
 comment "Generic NAND options"
 
 config SYS_NAND_BLOCK_SIZE
 	hex "NAND chip eraseblock size"
 	depends on ARCH_SUNXI || SPL_NAND_SUPPORT || TPL_NAND_SUPPORT
-	depends on !NAND_MXS && !NAND_DENALI_DT && !NAND_LPC32XX_MLC && !NAND_FSL_IFC
+	depends on !NAND_MXS && !NAND_DENALI_DT && !NAND_LPC32XX_MLC && \
+		!NAND_FSL_IFC && !NAND_MT7621
 	help
 	  Number of data bytes in one eraseblock for the NAND chip on the
 	  board. This is the multiple of NAND_PAGE_SIZE and the number of
@@ -556,7 +569,7 @@
 	depends on ARCH_SUNXI || NAND_OMAP_GPMC || NAND_LPC32XX_SLC || \
 		SPL_NAND_SIMPLE || (NAND_MXC && SPL_NAND_SUPPORT) || \
 		(NAND_ATMEL && SPL_NAND_SUPPORT) || SPL_GENERATE_ATMEL_PMECC_HEADER
-	depends on !NAND_MXS && !NAND_DENALI_DT && !NAND_LPC32XX_MLC
+	depends on !NAND_MXS && !NAND_DENALI_DT && !NAND_LPC32XX_MLC && !NAND_MT7621
 	help
 	  Number of data bytes in one page for the NAND chip on the
 	  board, not including the OOB area.