video: Rename CONFIG_DM_VIDEO to CONFIG_VIDEO

Now that all the old code is gone, rename this option. Driver model
migration is now complete.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/atmel/common/Makefile b/board/atmel/common/Makefile
index 6bc8cab..c046da7 100644
--- a/board/atmel/common/Makefile
+++ b/board/atmel/common/Makefile
@@ -6,4 +6,4 @@
 obj-y += board.o
 obj-$(CONFIG_I2C_EEPROM) += mac_eeprom.o
 obj-$(CONFIG_SPI_FLASH_SFDP_SUPPORT) += mac-spi-nor.o
-obj-$(CONFIG_DM_VIDEO) += video_display.o
+obj-$(CONFIG_VIDEO) += video_display.o