pci: avoid accidental clobbering of regs on some fdt platforms

Most pci controllers will just have a single reg for the config space,
but others (e.g., on Apple Silicon) may have more following that to
describe, e.g., controller port space. Bump the "ranges" rid space up
to avoid overriding these other memory resources.

Reviewed by: jhb
Differential Revision: https://reviews.freebsd.org/D43921