Fix 'call8: call target out of range' xtensa ld relaxation bug

Fix 'call8: call target out of range' xtensa ld relaxation bug

During link-time relaxation distance between cross-section call site and
its target may grow, producing 'call target out of range' error for
relaxed calls. Be more conservative when calculating whether or not a
callx can be converted to a straight call.

2014-09-23  Sterling Augustine  <augustine.sterling@gmail.com>

bfd/
    * elf32-xtensa.c (is_resolvable_asm_expansion): for cross-section
    call relaxation use furthermost addresses where call source and
    destination can be to check whether it's in the range of a direct
    call.