LinuxKPI: pci: harmonize #defines

In some blocks of #defines spacing, trailing \ and indentation of a
second line differed. Some of them are currently fine on a single
line but future additions may not fit in that scheme.
Harmonize them into a #define X\t\t\t...\\n<4 spaces>Y scheme.

No functional changes.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days
Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D51650