[ELFYAML] Add more SHT_xxx flags to the YAML section type mapping.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207904 91177308-0d34-0410-b5e6-96231b3b80d8
[ELFYAML] Group ELF header falgs to target specific blocks. Handle flags
which are corresponding to the current target read from the ELF file.

This fix cannot be tested until obj2yaml does not support ELF format.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207905 91177308-0d34-0410-b5e6-96231b3b80d8