powerpc/pseries: Use remove_memory() to remove memory

The memory remove code for powerpc/pseries should call remove_memory()
so that we are holding the hotplug_memory lock during memory remove
operations.

This patch updates the memory node remove handler to call remove_memory()
and adds a ppc_md.remove_memory() entry to handle pseries specific work
that is called from arch_remove_memory().

During memory remove in pseries_remove_memblock() we have to stay with
removing memory one section at a time. This is needed because of how memory
resources are handled. During memory add for pseries (via the probe file in
sysfs) we add memory one section at a time which gives us a memory resource
for each section. Future patches will aim to address this so will not have
to remove memory one section at a time.

Signed-off-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/machdep.h

@@ -282,6 +282,10 @@ struct machdep_calls {
 #ifdef CONFIG_ARCH_RANDOM
 	int (*get_random_long)(unsigned long *v);
 #endif
+
+#ifdef CONFIG_MEMORY_HOTREMOVE
+	int (*remove_memory)(u64, u64);
+#endif
 };
 
 extern void e500_idle(void);