- alpha_using_srm is #define'd for machine specific kernels, but
  is a real integer variable for generic Alpha kernels. Export
  it...

- The callback_* functions are _always_ there (they might be NOP
  functions owith generic kernels on non-SRM machines).

- srm_env can now be compiled on generic alpha kernels. An
  explicit check for SRM capability was always there:-)