[ELF] Adjust ELF header entry symbol value if this symbol is microMIPS encoded

To find an AtomLayout object for the given symbol I replace the
`Layout::findAtomAddrByName` method by `Layout::findAtomLayoutByName` method.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@223359 91177308-0d34-0410-b5e6-96231b3b80d8