sparc32: fix build, move inline function to .c file

Fix following build eroor:

  CC      arch/sparc/kernel/irq_32.o
In file included from arch/sparc/include/asm/smp.h:6:0,
                 from arch/sparc/include/asm/system_32.h:12,
                 from arch/sparc/include/asm/system.h:6,
                 from arch/sparc/include/asm/ptrace.h:235,
                 from arch/sparc/include/asm/thread_info_32.h:19,
                 from sparc/include/asm/thread_info.h:6,
                 from include/linux/thread_info.h:53,
                 from include/linux/preempt.h:9,
                 from include/linux/smp.h:34,
                 from include/linux/kernel_stat.h:4,
                 from arch/sparc/kernel/irq_32.c:14:
arch/sparc/include/asm/smp_32.h:82:19: error: static declaration of 'smp_call_function_single' follows non-static declaration
include/linux/smp.h:29:5: note: previous declaration of 'smp_call_function_single' was here

Bug is likely triggered by changes in include files.
The fix was obviously correct so I found no value in tracking
down the offending commit.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>