[llvm-mca] Move the routine that computes processor resource masks to its own file.

Function computeProcResourceMasks is used by the ResourceManager (owned by the
Scheduler) to compute resource masks for processor resources.  Before this
refactoring, there was an implicit dependency between the Scheduler and the
InstrBuilder. That is because InstrBuilder has to know about resource masks when
computing the set of processor resources consumed by a new instruction.

With this patch, the functionality that computes resource masks has been
extracted from the ResourceManager, and moved to a separate file (Support.h). 
This helps removing the dependency between the Scheduler and the InstrBuilder.

No functional change intended.

llvm-svn: 327973