x86/ioapic: Add proper checks to setp/enable_IO_APIC()

No point to have the same checks at every call site. Add them to the
functions, so they can be called unconditionally.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Tony Luck <tony.luck@intel.com>
Link: http://lkml.kernel.org/r/20150115211703.490719938@linutronix.de


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>