fsi: Add fsi_master_rescan()

We'll want non-core fsi code to trigger a rescan, so introduce a
non-static fsi_master_rescan() function. Use this for the existing
unscan/scan behaviour too.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Christopher Bostic <clbostic@linux.vnet.ibm.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>