arch: x86: fatal: If possible, print thread name in crash dump

It's relatively hard to figure out what thread a crash happens in
from the crash dump. E.g, it's usually not immediately possible to
find it out from linker map due to the fact that static symbols are
not there (https://sourceware.org/bugzilla/show_bug.cgi?id=16566

).

So, try to do it as easy if possible, by just printing thread name
in a dump, if thread names are enabled at all.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>