mmc: mediatek: add latch-ck support

some platform(eg.mt2701) does not support "stop clk fix", in
this case, need set correct latch-ck to avoid crc error caused
by stop clock block-internally.

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