dm: video: sandbox: Convert sandbox to use driver model for video

Now that driver model support is available, convert sandbox over to use it.
We can remove a few of the special hooks that sandbox currently has.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Anatolij Gustschin <agust@denx.de>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index 65184c8..898c5f4 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -76,6 +76,7 @@
 CONFIG_USB_STORAGE=y
 CONFIG_USB_KEYBOARD=y
 CONFIG_SYS_USB_EVENT_POLL=y
+CONFIG_DM_VIDEO=y
 CONFIG_VIDEO_SANDBOX_SDL=y
 CONFIG_CMD_DHRYSTONE=y
 CONFIG_TPM=y