powerpc/64s: allow for clang's objdump differences

Clang's objdump emits slightly different output from GNU's objdump,
causing a list of warnings to be emitted during relocatable builds.
E.g., clang's objdump emits this:

   c000000000000004: 2c 00 00 48  b  0xc000000000000030
   ...
   c000000000005c6c: 10 00 82 40  bf 2, 0xc000000000005c7c

while GNU objdump emits:

   c000000000000004: 2c 00 00 48  b    c000000000000030 <__start+0x30>
   ...
   c000000000005c6c: 10 00 82 40  bne  c000000000005c7c <masked_interrupt+0x3c>

Adjust llvm-objdump's output to remove the extraneous '0x' and convert
'bf' and 'bt' to 'bne' and 'beq' resp. to more closely match GNU
objdump's output.

Note that clang's objdump doesn't yet output the relocation symbols on
PPC.

Signed-off-by: Bill Wendling <morbo@google.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/191c67db31264b69cf6b566fd69851beb3dd0abb.1595630874.git.morbo@google.com