Introduce a use32bitAbi flag

Bug: 26874366

On Multiarch apps, it might be necessary to prioritize 32bit Abi ahead
of 64bit ones. The use32bitAbi flag enables this.

This CL also reverts the public api changes in  I2c1fd1d036efe72b28b5fe996416df69a583959f and Ie3ecea6d84e2cb1522e736a21c3a3a24ac62eb27. Previously
the same functionality was provided using a raw abi string that
utilized cpuabioverride flag.

Change-Id: Idce3cbfedd11ef9079ce8a2901e69d30b1cf9ef4