x86/emul: Rework emulator event injection

x86/emul: Rework emulator event injection

The emulator needs to gain an understanding of interrupts and exceptions
generated by its actions.

Move hvm_emulate_ctxt.{exn_pending,trap} into struct x86_emulate_ctxt so they
are visible to the emulator.  This removes the need for the
inject_{hw_exception,sw_interrupt}() hooks, which are dropped and replaced
with x86_emul_{hw_exception,software_event,reset_event}() instead.

For exceptions raised by x86_emulate() itself (rather than its callbacks), the
shadow pagetable and PV uses of x86_emulate() previously failed with
X86EMUL_UNHANDLEABLE due to the lack of inject_*() hooks.

This behaviour has changed, and such cases will now return X86EMUL_EXCEPTION
with event_pending set.  Until the callers of x86_emulate() have been updated
to inject events back into the guest, divert the event_pending case back into
the X86EMUL_UNHANDLEABLE path to maintain the same guest-visible behaviour.

No overall functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Tim Deegan <tim@xen.org>
Reviewed-by: Jan Beulich <jbeulich@suse.com>