powerpc/85xx: Fix SWIOTLB initalization for MPC85xxMDS boards

The code inside '#ifdef CONFIG_QUICC_ENGINE' makes the
mpc85xx_mds_setup_arch() return early if no QE nodes present,
and so SWIOTLB is never initialized.

This patch fixes the issue by moving SWIOTLB code above
QE.

Signed-off-by: Anton Vorontsov <avorontsov@mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>