util: consolidate duplicated error messages in pci.c

util: consolidate duplicated error messages in pci.c

This is nearly identical to an earlier patch for virnetlink.c.

There are special stub versions of all public functions in this file
that are compiled when the platform isn't linux. Each of these
functions had an almost identical message, differing only in the
function name included in the message. Since log messages already
contain the function name, we can just define a const char* with the
common part of the string, and use that same string for all the log
messages.

If nothing else, this at least makes for less strings that need
translating...