x86/emul: Always use fault semantics for software events

x86/emul: Always use fault semantics for software events

The common case is already using fault semantics out of x86_emulate(), as that
is how VT-x/SVM expects to inject the event (given suitable hardware support).

However, x86_emulate() returning X86EMUL_EXCEPTION and also completing a
register writeback is problematic for callers.

Switch the logic to always using fault semantics, and leave svm_inject_trap()
to fix up %eip if necessary.

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