drm/gpuvm: fix missing dependency to DRM_EXEC

In commit 50c1a36f ("drm/gpuvm: track/lock/validate external/evicted
objects") we started using drm_exec, but did not select DRM_EXEC in the
Kconfig for DRM_GPUVM, fix this.

Cc: Christian König <christian.koenig@amd.com>
Cc: Boris Brezillon <boris.brezillon@collabora.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Fixes: 50c1a36f ("drm/gpuvm: track/lock/validate external/evicted objects")
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240715135158.133287-1-dakr@redhat.com

drivers/gpu/drm/Kconfig

@@ -254,6 +254,7 @@ config DRM_EXEC
 config DRM_GPUVM
 	tristate
 	depends on DRM
+	select DRM_EXEC
 	help
 	  GPU-VM representation providing helpers to manage a GPUs virtual
 	  address space