tools: relocate-rela: Extract elf64 reloc to special function

tools: relocate-rela: Extract elf64 reloc to special function

Adding support for new type requires to change code layout that's why move
elf64 code to own function for easier maintenance.

It also solves the problem with not calling fclose in case of error.
Return value from rela_elf64 is saved to variable that's why fclose() is
called all the time.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/21763b80527521c85ca7d4ac64ad6ff4885409c8.1655299267.git.michal.simek@amd.com