Old toolchains don't know about slbfee and break the build, eg:
  {standard input}:37: Error: Unrecognized opcode: `slbfee.'

Fix it by using the macro version. We need to add an underscore
version that takes raw register numbers from the inline asm, rather
than our Rx macros.

Fixes: e15a4fea

 ("powerpc/64s/hash: Add some SLB debugging tests")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>