x86: unlock_ExtINT_logic() - fix section mismatch warnings

Fix following warning:
WARNING: arch/x86/kernel/built-in.o(.text+0x12cc9): Section mismatch in reference from the function unlock_ExtINT_logic()

unlock_ExtINT_logic() is only used by __init check_timer(). Annotate unlock_ExtINT_logic() witch __init.

Signed-off-by: Jacek Luczak <luczak.jacek@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>