[docs][llvm-dwarfdump] Add missing options and behaviour to documentation

This fixes https://bugs.llvm.org/show_bug.cgi?id=42185.

llvm-dwarfdump's documentation was missing a number of options and other
behaviours. This change tries to fix up the documentation by adding
these missing items.

Reviewed by: JDevlieghere

Differential Revision: https://reviews.llvm.org/D63217

llvm-svn: 363264