fs: move FMODE_UNSIGNED_OFFSET to fop_flags

This is another flag that is statically set and doesn't need to use up
an FMODE_* bit. Move it to ->fop_flags and free up another FMODE_* bit.

(1) mem_open() used from proc_mem_operations
(2) adi_open() used from adi_fops
(3) drm_open_helper():
    (3.1) accel_open() used from DRM_ACCEL_FOPS
    (3.2) drm_open() used from
    (3.2.1) amdgpu_driver_kms_fops
    (3.2.2) psb_gem_fops
    (3.2.3) i915_driver_fops
    (3.2.4) nouveau_driver_fops
    (3.2.5) panthor_drm_driver_fops
    (3.2.6) radeon_driver_kms_fops
    (3.2.7) tegra_drm_fops
    (3.2.8) vmwgfx_driver_fops
    (3.2.9) xe_driver_fops
    (3.2.10) DRM_GEM_FOPS
    (3.2.11) DEFINE_DRM_GEM_DMA_FOPS
(4) struct memdev sets fmode flags based on type of device opened. For
    devices using struct mem_fops unsigned offset is used.

Mark all these file operations as FOP_UNSIGNED_OFFSET and add asserts
into the open helper to ensure that the flag is always set.

Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jeff Layton <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
diff --git a/include/drm/drm_accel.h b/include/drm/drm_accel.h
index f4d3784..41c78b7 100644
--- a/include/drm/drm_accel.h
+++ b/include/drm/drm_accel.h
@@ -28,7 +28,8 @@
 	.poll		= drm_poll,\
 	.read		= drm_read,\
 	.llseek		= noop_llseek, \
-	.mmap		= drm_gem_mmap
+	.mmap		= drm_gem_mmap, \
+	.fop_flags	= FOP_UNSIGNED_OFFSET
 
 /**
  * DEFINE_DRM_ACCEL_FOPS() - macro to generate file operations for accelerators drivers