[llvm-readobj][ELF] New `-mips-plt-got` command line option to output
MIPS GOT section.

Patch reviewed by Rafael Espindola.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211150 91177308-0d34-0410-b5e6-96231b3b80d8