On aarch64, code is always little-endian, even when compiling
big-endian, so we need to force little-endian when reading
instructions.

Running the gcc C language testsuite, I get for an aarch64-elf target

# of expected passes            35433
# of unexpected failures        254
# of unsupported tests          131

and for an aarch64_be-elf target with the attached patch I get

# of expected passes            35200
# of unexpected failures        487
# of unsupported tests          131

so this simple patch gets us most of the way there.  I haven't tried
looking at the other problems yet.

I also have a dejagnu patch I wrote to make this work, which I will be
submitting to the dejagnu team shortly.

Jim