MPC8349EMDS: do not setup unused PCI clock outputs in PCI agent mode

When running in PCI agent mode, the PCI_CLK_OUT signals are not used, so do
not enable them. See the MPC8349EA Reference Manual, Section 4.4.2
"Clocking in PCI Agent Mode".

Signed-off-by: Ira W. Snyder <iws@ovro.caltech.edu>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>