Specs are available here:
https://www.nxp.com/docs/en/data-sheet/PCA9554_9554A.pdf
This is a simple model supporting the basic registers for GPIO
mode. The device also supports an interrupt output line but the
model does not yet support this.
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Glenn Miles <milesg@linux.vnet.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
