readelf: Fix symbol display for RELR relocs

readelf: Fix symbol display for RELR relocs

Filter symbols before binary searching for the right symbol to display
for a given address, such that only displayable symbols are present and
at most one per address.

The current logic does not handle multiple symbols for the same address
well if some of them are empty, the selected symbol is not stable with
respect to an unrelated symbol table change and on aarch64 often mapping
symbols are displayed which is not useful.

Filtering solves these problems at the cost of a linear scan of the
sorted symbol table.

The heuristic to select the best symbol likely could be improved, this
patch aims to improve symbol display for RELR without complex logic
such that the output is useful and stable for ld tests.