Drop CACHE_LINE_SIZE to 64 bytes on x86

The actual cache line size has always been 64 bytes.

The 128 number arose as an optimization for Core 2 era Intel processors. By
default (configurable in BIOS), these CPUs would prefetch adjacent cache
lines unintelligently. Newer CPUs prefetch more intelligently.

The latest Core 2 era CPU was introduced in September 2008 (Xeon 7400
series, "Dunnington"). If you are still using one of these CPUs, especially
in a multi-socket configuration, consider locating the "adjacent cache line
prefetch" option in BIOS and disabling it.

Reported by: mjg
Reviewed by: np
Discussed with: jhb
Sponsored by: Dell EMC Isilon