[Sparc][LEON] LEON Erratum fix. Insert NOP after LD or LDF instruction.

Due to an erratum in some versions of LEON, we must insert a NOP after any LD or LDF instruction to ensure the processor has time to load the value correctly before using it. This pass will implement that erratum fix.

The code will have no effect for other Sparc, but non-LEON processors.

Differential Review: http://reviews.llvm.org/D20353

llvm-svn: 270417