[POWERPC] Remove unneeded page_is_ram export

arch/powerpc/mm/mem.c exports page_is_ram, which is not used anywhere
that could be modular.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/mm/mem.c

@@ -80,7 +80,6 @@ int page_is_ram(unsigned long pfn)
 	return 0;
 #endif
 }
-EXPORT_SYMBOL(page_is_ram);
 
 pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
 			      unsigned long size, pgprot_t vma_prot)