powerpc/ps3: Fix compile error in ps3-lpm.c

Compiling with CONFIG_SMP = n and CONFIG_PS3_LPM != n gives this error:

drivers/ps3/ps3-lpm.c:838: error: implicit declaration of function 'get_hard_smp_processor_id'

This fixes it.  We have to include <asm/smp.h> rather than
<linux/smp.h> because the UP definition of get_hard_smp_processor_id()
is in <asm/smp.h>, and <linux/smp.h> only includes <asm/smp.h> if
CONFIG_SMP = y.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>