fsi: aspeed: Enable 23-bit addressing

In order to access more than the second hub link, 23-bit addressing is
required. The core provides the highest two bits of address as the slave
ID to the master.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
Acked-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Joel Stanley <joel@jms.id.au>