dm: mmc: Add a way to use driver model for MMC operations

The driver model conversion for MMC has moved in small steps. The first step
was to have an MMC device (CONFIG_DM_MMC). The second was to use a child
block device (CONFIG_BLK). The final one is to use driver model for MMC
operations (CONFIG_DM_MMC_OP). Add support for this.

The immediate priority is to make all boards that use DM_MMC also use those
other two options. This will allow them to be removed.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/mmc/Kconfig b/drivers/mmc/Kconfig
index c80efc3..b9662f9 100644
--- a/drivers/mmc/Kconfig
+++ b/drivers/mmc/Kconfig
@@ -16,6 +16,15 @@
 	  appear as block devices in U-Boot and can support filesystems such
 	  as EXT4 and FAT.
 
+config DM_MMC_OPS
+	bool "Support MMC controller operations using Driver Model"
+	depends on DM_MMC
+	help
+	  Driver model provides a means of supporting device operations. This
+	  option moves MMC operations under the control of driver model. The
+	  option will be removed as soon as all DM_MMC drivers use it, as it
+	  will the only supported behaviour.
+
 config MSM_SDHCI
 	bool "Qualcomm SDHCI controller"
 	depends on DM_MMC