x86: Consolidate irq entering inlines

smp.c and irq_work.c implement the same inline helper. Move it to
apic.h and use it everywhere.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>

diff --cc arch/x86/include/asm/apic.h
Simple merge

diff --cc arch/x86/kernel/irq_work.c
Simple merge

diff --cc arch/x86/kernel/smp.c
Simple merge