[lld][ELF] Add additional time trace categories

I noticed when running a large link with the --time-trace option that
there were several areas which were missing any specific time trace
categories (aside from the generic link/ExecuteLinker categories). This
patch adds new categories to fill most of the "gaps", or to provide more
detail than was previously provided.

Reviewed by: MaskRay, grimar, russell.gallop

Differential Revision: https://reviews.llvm.org/D90686