[llvm-objdump] Fix --file-headers (-f) option

Changed the format call to match the surrounding code. Previously it was
printing an unsigned int while the return type being printed was
long unsigned int or wider. This caused problems for big-endian systems
which were discovered on mips64.
Also, the printed address had less characters than it should because the
character count was directly obtained from the number of bytes in the
address.
The tests were adapted to fit this fix and now use longer addresses.

Patch by Milos Stojanovic.

Differential Revision: https://reviews.llvm.org/D53403

llvm-svn: 344818