events: drop arch_evtchn_inject()

events: drop arch_evtchn_inject()

Have the only user call vcpu_mark_events_pending() instead, at the same
time arranging for correct ordering of the writes (evtchn_pending_sel
should be written before evtchn_upcall_pending).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>