[llvm-readobj] Change "SHT_MIPS_DWARF" to "MIPS_DWARF"

Summary:
This is to be consistent with the display of other MIPS section types.
This string is also used by binutils-gdb/binutils/readelf.c:get_mips_section_type_name

Since we are here, reorder the two enum constatns because SHT_MIPS_DWARF < SHT_MIPS_ABIFLAGS.

Reviewers: jhenderson, atanasyan

Reviewed By: jhenderson

Subscribers: aprantl, sdardis, arichardson, rupprecht, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58496

llvm-svn: 354571