mmc: core: refactor debugfs code

Now, CONFIG_DEBUG_FS is scattered in various functions, to make code
clean centralized processing CONFIG_DEBUG_FS in mmc debugfs module.

Signed-off-by: Ye Bin <yebin10@huawei.com>
Link: https://lore.kernel.org/r/20221126102520.2824574-1-yebin@huaweicloud.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>