mmc: core: Add support for graceful host removal for eMMC

mmc: core: Add support for graceful host removal for eMMC

An mmc host driver may allow to unbind from its corresponding host device.
If an eMMC card is attached to the host, the mmc core will just try to cut
the power for it, without obeying to the eMMC spec.

Potentially this may damage the card and it may also prevent us from
successfully doing a re-initialization of it, which would typically happen
if/when we try to re-bind the mmc host driver.

To fix these problems, let's implement a graceful power-down of the card at
host removal.

Reported-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20250407152759.25160-5-ulf.hansson@linaro.org