x86/HVM: prevent infinite VM entry retries

This reverts the VMX side of commit 28b4baac ("x86/HVM: don't crash
guest upon problems occurring in user mode") and gets SVM in line with
the resulting VMX behavior. This is because Andrew validly says

"A failed vmentry is overwhelmingly likely to be caused by corrupt
 VMC[SB] state.  As a result, injecting a fault and retrying the the
 vmentry is likely to fail in the same way."

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Tim Deegan <tim@xen.org>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>