arch,cpu: Centralize the single arch CPU Simobject files. The way these were set up, there would be a conflict between SimObject files with the same name set up for different ISAs. This change creates a single file which tries to determine how many ISAs are enabled, and if there is exactly one, it creates a backwards compatible alias for the ISA specific CPU types. Change-Id: Iab358c2880d49222e814a98354c81d0f306fe1fc