mmc: mediatek: add support for MT7622 SoC

Just applying the existing logic and adding its own characteristics into
the space pointed by an extra entry of struct of_device_id to have support
of MT7622 SoC.

Signed-off-by: Chaotian Jing <chaotian.jing@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Tested-by: Jumin Li <jumin.li@mediatek.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>