x86/vmx: Use hvm_{get,set}_segment_register() rather than vmx_{get,set}_segment_regis...

x86/vmx: Use hvm_{get,set}_segment_register() rather than vmx_{get,set}_segment_register()

No functional change at this point, but this is a prerequisite for forthcoming
functional changes.

Make vmx_get_segment_register() private to vmx.c like all the other Vendor
get/set functions.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>