i2c: Deprecate the legacy gpio drivers

The legacy pcf8574 and pcf8575 drivers should be avoided
on systems using the new gpiolib code, and generally deprecated
in the same way the legacy pca9539 driver is deprecated.

Also, correct the pca9539 deprecation to match the current name
of the preferred driver:  pca953x, supporting several more chips.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>