mtd: nand: MTD_NAND_ECC_MEDIATEK should depend on ARCH_MEDIATEK

The MediaTek Hardware ECC Engine is only present on MediaTek MT27xx and
MT76xx SoCs.  The driver for this engine is a dependency for the
MediaTek NAND controller (MTD_NAND_MTK) and the MediaTek SPI NAND Flash
Interface (SPI_MTK_SNFI) drivers, both of which already depend on
ARCH_MEDIATEK.

Hence add a dependency on ARCH_MEDIATEK to the Hardware ECC Engine
driver, too, to prevent asking the user about this driver when
configuring a kernel without MediaTek SoC support.

Fixes: 4fd62f15 ("mtd: nand: make mtk_ecc.c a separated module")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/bb9568e825d4bc7506870b03836baa91bcc4b725.1652104136.git.geert+renesas@glider.be