x86: Enhance x86_handle_events to x86_check_events

x86: Enhance x86_handle_events to x86_check_events

There is now quite some commonality between svm and vmx when it comes to
checking for pending events. Move those parts into x86_check_events,
which becomes the extended version of x86_handle_events. Only a small
difference is now left behind in vmx_check_events(): the preemption
timer has to be disabled before the check.

Just like x86_handle_events, also x86_check_events only works against
the caller's CPU. So remove the cpu_data parameter at this chance.

We can remove the "sipi_vector = -1" after x86_enter_wait_for_sipi now
because we no longer return that value from x86_check_events, and
sipi_vector is not evaluated elsewhere because cpu_data->wait_for_sipi
is true.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>