twi: Working code for being able to switch between USCI_B0 and USCI_B1

Comment out code in wiring_digial.c related to the port map controller,
which is being used for the F5529, but the code makes the USCI_B1 being
initialized to "bus busy". This might very well be caused by me not
sending correct input into the pinMode_int method.

By just uncommenting the "//#define USE_USCI_B1 1" line, you are able
to use the USCI_B1 module, instead of USCI_B0.

There are also some general I2C improvements, like following the order
suggested in MSP430 Family Guide on how to init I2C. And avoiding
setting stuff in "two_readFrom" and "twi_writeTo" that has already
been set in the "init" method.

There is still need for improvements before the code can be merged.
Ideally, I want to be able to use both modules B0 and B1 from my
sketch, so the Wire/twi needs to support having both modules in
use at the same time.