tools: relocate-rela: Fix BE symtab handling

The symtab contains data in target endianness, convert the data to
native endianness before doing any operations and on them, and back
to target endianness before updating the bin file.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Tested-by: Michal Simek <michal.simek@amd.com> # microblaze, arm64
Reviewed-by: Angelo Dureghello <angelo@kernel-space.org>