Test assembler driver utilities.

Rationale:
Quis custodiet ipsos custodes?

Therefore, it is good to make sure that the drivers
used to test the assembler are doing what is expected.
This also prepares some upcoming improvements wrt.
addressing modes and different register sizes.

Bug: 18380245
Bug: 18380559
Bug: 18380245

Test: assembler_x86[_64]_test

Change-Id: Iadc269c14cb9e15941ec66c362d59d42e9017001