mtd: rawnand: denali_dt: use UCLASS_MTD instead of UCLASS_MISC

UCLASS_MTD is a better fit for NAND drivers.

Make NAND_DENALI_DT depend on DM_MTD, which is needed to compile
drivers/mtd/mtd-uclass.c

Also, make ARCH_UNIPHIER select DM_MTD because all the defconfig
of this platform enables NAND_DENALI_DT.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 1236315..f04b6a6 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1548,6 +1548,7 @@
 	select DM_GPIO
 	select DM_I2C
 	select DM_MMC
+	select DM_MTD
 	select DM_RESET
 	select DM_SERIAL
 	select DM_USB