x86/apic: Convert other overrides to apic_update_callback()

Convert all places which just assign a new function directly to the apic
callback to use apic_update_callback() which prepares for using static
calls.

Mark snp_set_wakeup_secondary_cpu() and kvm_setup_pv_ipi() __init, as they
are only invoked from init code and otherwise trigger a section mismatch as
they are now invoking a __init function.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Michael Kelley <mikelley@microsoft.com>
Tested-by: Sohil Mehta <sohil.mehta@intel.com>
Tested-by: Juergen Gross <jgross@suse.com> # Xen PV (dom0 and unpriv. guest)