drm/debugfs: Output client_id in in drm_clients_info

client_id is a unique id used by fdinfo. Having it listed in 'clients'
output means a userspace application can correlate the fields, eg:
given a fdinfo id get the fdinfo name.

Geiven that client_id is a uint64_t, we use a %20llu printf format to
keep the output aligned (20 = digit count of the biggest uint64_t).

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Signed-off-by: Philipp Stanner <phasta@kernel.org>
Link: https://lore.kernel.org/r/20250526125505.2360-2-pierre-eric.pelloux-prayer@amd.com