mmc: sdhci: Introduce new flag SDHCI_USING_RETUNING_TIMER

Add a new flag of SDHCI_USING_RETUNING_TIMER to represent if the host
is using a retuning timer for the card inserted.

This flag is set when the host does tuning the first time for the card
and the host's retuning mode is 1. This flag is used afterwards whenever
needs to decide if the host is currently using a retuning timer.

This flag is cleared when the card is removed in sdhci_reinit.

The set/clear of the flag and the start/stop of the retuning timer is
associated with the card's init/remove time, so there is no need to
touch it when the host is to be removed as at that time the card should
have already been removed.

Signed-off-by: Aaron Lu <aaron.lu@amd.com>
Reviewed-by: Girish K S <girish.shivananjappa@linaro.org>
Reviewed-by: Philip Rakity <prakity@marvell.com>
Signed-off-by: Chris Ball <cjb@laptop.org>