mpc5200: digsy_mtc: fix detection of Coral-PA

A delay of approximately 250 ms after PCI bus reset in
pci_mpc5xxx_init() is needed to recognize the Coral-PA
controller on the graphic extention board.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Acked-by: Detlev Zundel <dzu@denx.de>