Promote pci_scan() to public shared PCI method

[Joel Sherrill]

The new libbsp/shared/pci/pci_find_device.c is based upon the pcifinddevice.c from PowerPC and MIPS BSPs. There were multiple copies of the same code across multiple BSPs. This ticket is the clean up required to remove the last user of a copy and then have only one copy.

It renamed BSP_pciScan() to pci_scan() and made it a static routine. This method should be made public in the shared implementation, uses of BSP_pciScan() modified to use pci_scan(), and the impacted BSPs' Makefile.am modified to use the shared pci_find_device.c.

BSP_pciScan() is used by some component(s) used by each of the following BSPs:

beatnik
motorola_shared
mvme3100

This impacts the following BSPs.

$ grep -rl BSP_pciScan .
./c/src/lib/libbsp/powerpc/beatnik/pci/motload_fixup.c
./c/src/lib/libbsp/powerpc/beatnik/network/support/bsp_attach.c
./c/src/lib/libbsp/powerpc/mvme3100/pci/detect_host_bridge.c
./c/src/lib/libbsp/powerpc/shared/pci/pci.h
./c/src/lib/libbsp/powerpc/shared/pci/pcifinddevice.c