x86/apic: Share common IPI helpers

The 64bit implementations need the same wrappers around
__default_send_IPI_shortcut() as 32bit.

Move them out of the 32bit section.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190722105220.951534451@linutronix.de