[PowerPC64LE] Endian fixes for opal_pci.c.

Since OPAL runs in big endian, any data being passed back and forth
via memory instead of registers needs to be byteswapped.

From my notes during development:

"A good way to find candidates is to look for vtophys() in opal_call()
parameters. The memory being passed will be written into in BE."

Sponsored by: Tag1 Consulting, Inc.