video: adf: Fix modular build

Builds with ADF configured as module fail the following errors.

ERROR: "adf_fops" [drivers/video/adf/adf_sysfs.ko] undefined!
ERROR: "adf_obj_sysfs_find" [drivers/video/adf/adf_fops.ko] undefined!
ERROR: "adf_buffer_cleanup" [drivers/video/adf/adf_fops.ko] undefined!
ERROR: "adf_attachment_validate" [drivers/video/adf/adf_client.ko] undefined!
ERROR: "adf_attachment_find" [drivers/video/adf/adf_client.ko] undefined!
ERROR: "adf_buffer_mapping_cleanup" [drivers/video/adf/adf_client.ko] undefined!
ERROR: "adf_attachment_free" [drivers/video/adf/adf_client.ko] undefined!
ERROR: "adf_obj_find_event_refcount" [drivers/video/adf/adf_client.ko] undefined!
ERROR: "adf_file_queue_event" [drivers/video/adf/adf.ko] undefined!
ERROR: "adf_interface_sysfs_init" [drivers/video/adf/adf.ko] undefined!
ERROR: "adf_interface_sysfs_destroy" [drivers/video/adf/adf.ko] undefined!
ERROR: "adf_device_sysfs_init" [drivers/video/adf/adf.ko] undefined!
ERROR: "adf_device_sysfs_destroy" [drivers/video/adf/adf.ko] undefined!
ERROR: "adf_sysfs_destroy" [drivers/video/adf/adf.ko] undefined!
ERROR: "adf_overlay_engine_sysfs_init" [drivers/video/adf/adf.ko] undefined!
ERROR: "adf_overlay_engine_sysfs_destroy" [drivers/video/adf/adf.ko] undefined!
ERROR: "adf_sysfs_init" [drivers/video/adf/adf.ko] undefined!

If ADF is configured as module, each of the object files ends up being
a separate module. Since the functions are used across the various files
but not exported, this results in the observed build errors.
Modify the Makefile to create a single module instead.

Fixes: 066a50cee536 ("video: add atomic display framework")
Signed-off-by: Guenter Roeck <groeck@chromium.org>
diff --git a/drivers/video/adf/Makefile b/drivers/video/adf/Makefile
index 78d0915..cdf34a6 100644
--- a/drivers/video/adf/Makefile
+++ b/drivers/video/adf/Makefile
@@ -2,13 +2,15 @@
 
 CFLAGS_adf.o := -I$(src)
 
-obj-$(CONFIG_ADF) += adf.o \
+obj-$(CONFIG_ADF) += adf_core.o
+
+adf_core-y := adf.o \
 	adf_client.o \
 	adf_fops.o \
 	adf_format.o \
 	adf_sysfs.o
 
-obj-$(CONFIG_COMPAT) += adf_fops32.o
+adf_core-$(CONFIG_COMPAT) += adf_fops32.o
 
 obj-$(CONFIG_ADF_FBDEV) += adf_fbdev.o