arc: fix relocation for big-endian target

arc: fix relocation for big-endian target

In case of little-endian ARC700 instructions (which may include target
address) are encoded as middle-endian. That's why it's required to swap
bytes after read and ten right before write back.

But in case of big-endian ARC700 instructions are encoded as a plain
big-endian. Thus no need for byte swapping.

Signed-off-by: Alexey Brodkin <[email protected]>
Cc: Francois Bedard <[email protected]>
Cc: Tom Rini <[email protected]>
cc: Noam Camus <[email protected]>