mmc: sdhci: Add platform suspend/resume hooks.

Some platforms require saving/restoring registers across suspend/resume;
this hook allows them to do that inside their driver.

Signed-off-by: Chris Ball <cjb@laptop.org>
diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index 8d66706..1f5888b 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -2379,6 +2379,9 @@
 	int ret;
 	bool has_tuning_timer;
 
+	if (host->ops->platform_suspend)
+		host->ops->platform_suspend(host);
+
 	sdhci_disable_card_detection(host);
 
 	/* Disable tuning since we are suspending */
@@ -2429,6 +2432,9 @@
 	ret = mmc_resume_host(host->mmc);
 	sdhci_enable_card_detection(host);
 
+	if (host->ops->platform_resume)
+		host->ops->platform_resume(host);
+
 	/* Set the re-tuning expiration flag */
 	if ((host->version >= SDHCI_SPEC_300) && host->tuning_count &&
 	    (host->tuning_mode == SDHCI_TUNING_MODE_1))