Instead of setting the Xen PV apic driver very early during boot, just use
the standard apic driver probing by setting an appropriate
x86_init.irqs.intr_mode_init callback.

At the same time eliminate xen_apic_check() which has never been used.

The #ifdef CONFIG_X86_LOCAL_APIC around the call of xen_init_apic()
can be removed, too, as CONFIG_XEN depends on CONFIG_X86_LOCAL_APIC.
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
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)
Link: https://lore.kernel.org/lkml/aa086365-fd02-210f-67c6-5c9175c0dfee@suse.com