dm: mmc: rockchip: Enable CONFIG_DM_MMC_OPS for all boards

Enable this option to move rockchip over to use driver model for MMC
operations.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 8004c17..585b408 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -850,6 +850,7 @@
 	select DM_GPIO
 	select DM_I2C
 	select DM_MMC
+	select DM_MMC_OPS
 	select DM_SERIAL
 	select DM_SPI
 	select DM_SPI_FLASH