83xx: PCI agent mode fixes for multi-board systems

83xx: PCI agent mode fixes for multi-board systems

When running a system with 2 or more MPC8349EMDS boards in PCI agent mode,
the boards will lock up the PCI bus by scanning against each other.

The boards lock against each other by trying to access the PCI bus before
clearing their configuration lock bit. Both boards end up in a loop,
sending and receiving "Target Not Ready" messages forever.

When running in PCI agent mode, the scanning now takes place after the
boards have cleared their configuration lock bit.

Also, add a missing declaration to the mpc83xx.h header file, fixing a
build warning.

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