drm/tests: shmem: Hold reservation lock around vmap/vunmap

In the Linux kernel, the following vulnerability has been resolved: drm/tests: shmem: Hold reservation lock around vmap/vunmap Acquire and release the GEM object's reservation lock around vmap and vunmap operations. The tests use vmap_locked, which led to errors such as show below. [ 122.292030] WARNING: CPU: 3 PID: 1413 at drivers/gpu/drm/drm_gem_shmem_helper.c:390 drm_gem_shmem_vmap_locked+0x3a3/0x6f0 [ 122.468066] WARNING: CPU: 3 PID: 1413 at drivers/gpu/drm/drm_gem_shmem_helper.c:293 drm_gem_shmem_pin_locked+0x1fe/0x350 [ 122.563504] WARNING: CPU: 3 PID: 1413 at drivers/gpu/drm/drm_gem_shmem_helper.c:234 drm_gem_shmem_get_pages_locked+0x23c/0x370 [ 122.662248] WARNING: CPU: 2 PID: 1413 at drivers/gpu/drm/drm_gem_shmem_helper.c:452 drm_gem_shmem_vunmap_locked+0x101/0x330 Only export the new vmap/vunmap helpers for Kunit tests. These are not interfaces for regular drivers.