[lld][ELF] Differentiate between Note sections(RW/RO)

It looks like there is a possibility of seeing RO/RW note sections
and we would need to create an appropriate RO/RW segment associated
with them.

Adds a test too.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@189907 91177308-0d34-0410-b5e6-96231b3b80d8