x86/svm: Drop the suggestion of Long Mode Segment Limit support

x86/svm: Drop the suggestion of Long Mode Segment Limit support

Because of a bug in 2010, LMSL support isn't available to guests.

c/s f2c608444 noticed but avoided fixing the issue for migration reasons.  In
addition to migration problems, changes to the segmentation logic for
emulation would be needed before the feature could be enabled.

This feature is entirely unused by operating systems (probably owing to its
semantics which only cover half the segment registers), and no one has
commented on its absence from Xen.  As supporting it would involve a large
amount of effort, it seems better to remove the code entirely.

If someone finds a valid usecase, we can resurrecting the code and
implementing the remaining parts, but I doubt anyone will.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>