mmc: add a card-event host operation

Some hosts need to perform additional actions upon card insertion or
ejection. Add a host operation to be called from card detection handlers.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Reviewed-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>

include/linux/mmc/host.h

@@ -136,6 +136,7 @@ struct mmc_host_ops {
 	void	(*enable_preset_value)(struct mmc_host *host, bool enable);
 	int	(*select_drive_strength)(unsigned int max_dtr, int host_drv, int card_drv);
 	void	(*hw_reset)(struct mmc_host *host);
+	void	(*card_event)(struct mmc_host *host);
 };
 
 struct mmc_card;