mfd: tc3589x: Detect the precise version

Instead of detecting the "tc3589x" and hard-coding the number of
GPIO pins to 24, encode all the possible subtypes and set the
number of GPIO pins from the type.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>