gpio: Merge TCA6416 & TCA6408 drivers into TCA64XX

This merges TCA6416, TCA6408 drivers and adds PCA9555 support.
They handle 8 pin and 16 pin ICs with basic INPUT/OUTPUT functionality.
The register map is fairly similar so there is no point in having two
separate drivers.

Reviewed by: kd
Obtained from: Semihalf
Differential Revision: https://reviews.freebsd.org/D36559