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/Makefile b/drivers/mtd/nand/raw/Makefile
index e3f6b90..f278f31 100644
--- a/drivers/mtd/nand/raw/Makefile
+++ b/drivers/mtd/nand/raw/Makefile
@@ -72,6 +72,7 @@
 obj-$(CONFIG_NAND_STM32_FMC2) += stm32_fmc2_nand.o
 obj-$(CONFIG_CORTINA_NAND) += cortina_nand.o
 obj-$(CONFIG_ROCKCHIP_NAND) += rockchip_nfc.o
+obj-$(CONFIG_NAND_MT7621) += mt7621_nand.o
 
 else  # minimal SPL drivers
 
@@ -80,5 +81,6 @@
 obj-$(CONFIG_NAND_MXC) += mxc_nand_spl.o
 obj-$(CONFIG_NAND_MXS) += mxs_nand_spl.o mxs_nand.o
 obj-$(CONFIG_NAND_SUNXI) += sunxi_nand_spl.o
+obj-$(CONFIG_NAND_MT7621) += mt7621_nand_spl.o mt7621_nand.o
 
 endif # drivers