xfs: add a separate tracepoint for stealing an open zone for GC

xfs: add a separate tracepoint for stealing an open zone for GC

The case where we have to reuse an already open zone warrants a different
trace point vs the normal opening of a GC zone.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>