mmc: Support driver model in TPL

Some boards want to use DM_MMC in TPL so add an option for that.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/mmc/Kconfig b/drivers/mmc/Kconfig
index 982e84d..22c6568 100644
--- a/drivers/mmc/Kconfig
+++ b/drivers/mmc/Kconfig
@@ -61,6 +61,17 @@
 	  appear as block devices in U-Boot and can support filesystems such
 	  as EXT4 and FAT.
 
+config TPL_DM_MMC
+	bool "Enable MMC controllers using Driver Model in TPL"
+	depends on TPL_DM && DM_MMC
+	select TPL_BLK
+	help
+	  This enables the MultiMediaCard (MMC) uclass which supports MMC and
+	  Secure Digital I/O (SDIO) cards. Both removable (SD, micro-SD, etc.)
+	  and non-removable (e.g. eMMC chip) devices are supported. These
+	  appear as block devices in U-Boot and can support filesystems such
+	  as EXT4 and FAT.
+
 if MMC
 
 config MMC_SDHCI_ADMA_HELPERS