drm: add DRM_SET_CLIENT_NAME ioctl

Giving the opportunity to userspace to associate a free-form
name with a drm_file struct is helpful for tracking and debugging.

This is similar to the existing DMA_BUF_SET_NAME ioctl.

Access to client_name is protected by a mutex, and the 'clients' debugfs
file has been updated to print it.

Userspace MR to use this ioctl:
   virgl/virglrenderer!1428



If the string passed by userspace contains chars that would mess up output
when it's going to be printed (in dmesg, fdinfo, etc), -EINVAL is returned.

A 0-length string is a valid use, and clears the existing name.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241003124506.470931-2-pierre-eric.pelloux-prayer@amd.com


Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>