libi2cdriver: add functions for IC register access
Many i2c device drivers used similar code to access registers on
the ICs they drive. This commit implements that functionality in
libi2cdriver and updates the drivers to use the library instead of
their own register access functions. The net result is 375+ fewer
lines of code and less work for people developing new drivers.
The two exceptions were cat24c256 and parts of tda19988. They access
the bus in uncommon ways. It doesn't make sense at this time to
move their read/write functions into libi2cdriver.