powerpc/mm: Build fix for non SPARSEMEM_VMEMAP config

We can use pfn_to_page() in realmode for other configs. Hence remove the
CONFIG_FLATMEM ifdef.

Fixes: 8e0861fa3c4e ("powerpc: Prepare to support kernel handling of IOMMU map/unmap")
Cc: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
[mpe: Also fix up the #endif comment]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/init_64.c

@@ -356,7 +356,7 @@ struct page *realmode_pfn_to_page(unsigned long pfn)
 }
 EXPORT_SYMBOL_GPL(realmode_pfn_to_page);
 
-#elif defined(CONFIG_FLATMEM)
+#else
 
 struct page *realmode_pfn_to_page(unsigned long pfn)
 {
@@ -365,7 +365,7 @@ struct page *realmode_pfn_to_page(unsigned long pfn)
 }
 EXPORT_SYMBOL_GPL(realmode_pfn_to_page);
 
-#endif /* CONFIG_SPARSEMEM_VMEMMAP/CONFIG_FLATMEM */
+#endif /* CONFIG_SPARSEMEM_VMEMMAP */
 
 #ifdef CONFIG_PPC_STD_MMU_64
 static bool disable_radix;