cpus: add handle_interrupt to the CpusAccel interface

cpus: add handle_interrupt to the CpusAccel interface

kvm: uses the generic handler
qtest: uses the generic handler
whpx: changed to use the generic handler (identical implementation)
hax: changed to use the generic handler (identical implementation)
hvf: changed to use the generic handler (identical implementation)
tcg: adapt tcg-cpus to point to the tcg-specific handler

Signed-off-by: Claudio Fontana <cfontana@suse.de>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>