dm: mmc: spl: Use the legacy block interface in SPL

Bring this in for SPL so that we can use generic code for loading from
block devices.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/Makefile

@@ -37,6 +37,7 @@ obj-$(CONFIG_SPL_USB_HOST_SUPPORT) += usb/host/
 obj-$(CONFIG_OMAP_USB_PHY) += usb/phy/
 obj-$(CONFIG_SPL_SATA_SUPPORT) += block/
 obj-$(CONFIG_SPL_USB_HOST_SUPPORT) += block/
+obj-$(CONFIG_SPL_MMC_SUPPORT) += block/
 
 else