EDAC, pnd2_edac: Fix !EDAC_DEBUG build

Provide debugfs function stubs when EDAC_DEBUG is not enabled so that we
don't fail the build:

  drivers/edac/pnd2_edac.c: In function ‘pnd2_init’:
  drivers/edac/pnd2_edac.c:1521:2: error: implicit declaration of function ‘setup_pnd2_debug’ [-Werror=implicit-function-declaration]
    setup_pnd2_debug();
    ^
  drivers/edac/pnd2_edac.c: In function ‘pnd2_exit’:
  drivers/edac/pnd2_edac.c:1529:2: error: implicit declaration of function ‘teardown_pnd2_debug’ [-Werror=implicit-function-declaration]
    teardown_pnd2_debug();
    ^

Signed-off-by: Borislav Petkov <bp@suse.de>