percpu: add dummy pcpu_lpage_remapped() for !CONFIG_SMP

!CONFIG_SMP was missing pcpu_lpage_remapped() definition causing build
failure.  Add dummy implementation.  This was discovered by linux-next
testing.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>