x86/apic: Wire up single IPI for apic_physflat

Use the default implementation.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Borislav Petkov <bp@alien.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Travis <travis@sgi.com>
Cc: Daniel J Blueman <daniel@numascale.com>
Link: http://lkml.kernel.org/r/20151104220849.055046864@linutronix.de

arch/x86/kernel/apic/apic_flat_64.c

@@ -281,6 +281,7 @@ static struct apic apic_physflat =  {
 
 	.cpu_mask_to_apicid_and		= default_cpu_mask_to_apicid_and,
 
+	.send_IPI			= default_send_IPI_single_phys,
 	.send_IPI_mask			= default_send_IPI_mask_sequence_phys,
 	.send_IPI_mask_allbutself	= default_send_IPI_mask_allbutself_phys,
 	.send_IPI_allbutself		= physflat_send_IPI_allbutself,