fsi: Add aliased device numbering

The I2C and SPI subsystems can use an aliased name to number the device.
Add similar support to the FSI subsystem for any device type.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
Link: https://lore.kernel.org/r/20230612195657.245125-3-eajames@linux.ibm.com


Signed-off-by: Joel Stanley <joel@jms.id.au>