tools: relocate-rela: Check that relocation works only for EM_AARCH64

Relocation support is only for EM_AARCH64 that's why check machine type to
make sure that the code will never run on any unsupported one.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/36f26c8752335239344b265e5ddedad10e9cac8b.1655299267.git.michal.simek@amd.com