x86/apic: Simplify enable_IR_x2apic(), remove try_to_enable_IR()

The following commit:

  2e63ad4b ("x86/apic: Do not init irq remapping if ioapic is disabled")

... added a check for skipped IO-APIC setup to enable_IR_x2apic(), but this
check is also duplicated in try_to_enable_IR() - and it will never succeed in
calling irq_remapping_enable().

Remove the whole irq_remapping_enable() complication: if the IO-APIC is
disabled we cannot enable IRQ remapping.

Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bp@alien8.de
Cc: nicstange@gmail.com
Cc: wanpeng.li@hotmail.com
Link: http://lkml.kernel.org/r/1487841401-1543-1-git-send-email-douly.fnst@cn.fujitsu.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>