This patch fixs eMMC-Access on mt7622/Bpi-64.
Before we got these Errors on mounting eMMC ion R64:
[   48.664925] blk_update_request: I/O error, dev mmcblk0, sector 204800 op 0x1:(WRITE)
flags 0x800 phys_seg 1 prio class 0
[   48.676019] Buffer I/O error on dev mmcblk0p1, logical block 0, lost sync page write

This patch adds a optional reset management for msdc.
Sometimes the bootloader does not bring msdc register
to default state, so need reset the msdc controller.

Cc: <stable@vger.kernel.org> # v5.4+
Fixes: 966580ad ("mmc: mediatek: add support for MT7622 SoC")
Signed-off-by: Wenbin Mei <wenbin.mei@mediatek.com>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Tested-by: Frank Wunderlich <frank-w@public-files.de>
Link: https://lore.kernel.org/r/20200814014346.6496-4-wenbin.mei@mediatek.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>