um: Serve io_remap_pfn_range()

At some places io_remap_pfn_range() is needed.
UML has to serve it like all other archs do.
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/include/asm/pgtable.h

@@ -69,6 +69,8 @@ extern unsigned long end_iomem;
 #define PAGE_KERNEL	__pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY | _PAGE_ACCESSED)
 #define PAGE_KERNEL_EXEC	__pgprot(__PAGE_KERNEL_EXEC)
 
+#define io_remap_pfn_range	remap_pfn_range
+
 /*
  * The i386 can't do page protection for execute, and considers that the same
  * are read.