[Sparc][LEON] Add UMAC and SMAC instruction support for Sparc LEON subtargets

This change adds SMAC (signed multiply-accumulate) and UMAC (unsigned multiply-accumulate) for LEON subtargets of the Sparc processor.

The new files LeonFeatures.td and leon-instructions.ll will both be expanded in future, so I want to leave them separate as small files for this review, to be expanded in future check-ins.

Note: The functions are provided only for inline-assembly provision. No DAG selection is provided.

Differential Revision: http://reviews.llvm.org/D19911

llvm-svn: 268908