[llvm-objcopy] Add elf32-sparc and elf32-sparcel target

Summary:
The "sparc"/"sparcel" architectures appears in ArchMap (used by -B option) but not in OutputFormatMap (used by -I/-O option). Add their targets into OutputFormatMap for consistency.

Note that AFAIK there're no targets for 32-bit little-endian SPARC ("elf32-sparcel") in GNU binutils.

Reviewers: espindola, alexshap, rupprecht, jhenderson, compnerd, jakehehrlich

Reviewed By: jhenderson, compnerd, jakehehrlich

Subscribers: jyknight, emaste, arichardson, fedor.sergeev, jakehehrlich, MaskRay, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63238

llvm-svn: 363524