This adds support for 16 bit io expander pcf8575. The driver is basically
the same as for pcf8574 however it is for 16 bits instead of 8 bits. Since
pcf8575 and pcf8574 can be both used on the same i2c bus the driver for
pcf8575 is implemented in a different file to reduce the code size
and complexity and to have less if statements in the driver.
Signed-off-by: Michal Lenc <michallenc@seznam.cz>
