x86: Fix some bugs with KVM in SE mode on Intel machines.

x86: Fix some bugs with KVM in SE mode on Intel machines.

The granularity bit should be set since the segment limit should be
interpreted as a number of pages, not bytes.

A comment indicates that NX support is enabled, but the bit wasn't
being set. That's now set to be consistent with FS mode.

The SVME bit is now turned off, since Intel CPUs don't have SVME, and
enabling it apparently makes them upset.

Also disable CR4 bits which enable features neither gem5 nor apparently
my workstation support.

Change-Id: I72d5a07871dede8763b0dd188a52fe5eb6bde6ea
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23361
Reviewed-by: Ayaz Akram <yazakram@ucdavis.edu>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>