i2c-sunxi: Fix support for TWI3 and TWI4 on A20

Although Hans had introduced support for TWI3 and TWI4, the functions
handling the clocks and pins were limited to only TWI0-2. Let's fix the
clock lists to include the new A20 names, as well as generalize the pin
functions to handle all 5 buses.

Reported-by: Sertac Tüllük <stulluk@gmail.com>
Signed-off-by: Emilio López <turl@linux-sunxi.org>