[POWERPC] Add spinlock to request_phb_iospace()

request_phb_iospace() can be called from different CPUs at init
time (at least with my next patch) and thus needs a spinlock.
As for the next patch, this is a temporary workaround for 2.6.22
issues until my rewrite of IO mappings is ready (for 2.6.23)

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/mm/pgtable_64.c

@@ -322,15 +322,19 @@ EXPORT_SYMBOL(__ioremap);
 EXPORT_SYMBOL(iounmap);
 EXPORT_SYMBOL(__iounmap);
 
+static DEFINE_SPINLOCK(phb_io_lock);
+
 void __iomem * reserve_phb_iospace(unsigned long size)
 {
 	void __iomem *virt_addr;
 
 	if (phbs_io_bot >= IMALLOC_BASE) 
 		panic("reserve_phb_iospace(): phb io space overflow\n");
 
+	spin_lock(&phb_io_lock);
 	virt_addr = (void __iomem *) phbs_io_bot;
 	phbs_io_bot += size;
+	spin_unlock(&phb_io_lock);
 
 	return virt_addr;
 }