powerpc: Add missing sparsemem.h include

arch/powerpc/platforms/pseries/hotplug-memory.c uses
remove_section_mapping() but doesn't include sparsemem.h which defines
it.  This can cause compilation fails for some configs.
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/pseries/hotplug-memory.c

@@ -14,6 +14,7 @@
 #include <asm/firmware.h>
 #include <asm/machdep.h>
 #include <asm/pSeries_reconfig.h>
+#include <asm/sparsemem.h>
 
 static int pseries_remove_lmb(unsigned long base, unsigned int lmb_size)
 {