EMMC: ascend customized emmc host

ascend inclusion
category: feature
feature: Ascend emmc adaption
bugzilla: https://gitee.com/openeuler/kernel/issues/I4F4LL


CVE: NA

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To identify Ascend HiSilicon emmc chip, we add a customized property
to dts. In this patch we add an interface to read this property. At
the same time, we provided a switch, which is CONFIG_ASCEND_HISI_MMC,
for you to get rid of our modifications.

Signed-off-by: zhangguijiang <zhangguijiang@huawei.com>
Reviewed-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>