i2c: mux: pca954x: remove support for unused platform data

There are no in-tree users of the pca954x platform data and the
per-channel deselect configuration complicates efforts to export the
configuration to user-space in a way that could be applied to other
muxes. Therefore, remove support for the pca954x platform data.

Signed-off-by: Robert Shearman <robert.shearman@att.com>
Signed-off-by: Peter Rosin <peda@axentia.se>