ibm_newemac: Fix new MAL feature handling

Support for new features needed by the PPC 405EZ boards
introduced some errors in the MAL and EMAC feature handling.
This broke 'allmodconfig' builds as CONFIG_PPC_DCR_NATIVE is
not set for those.

This patch fixes these errors by wrapping the code in the
appropriate #ifdefs.

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>