sh: add EXPORT_SYMBOL(min_low_pfn) and EXPORT_SYMBOL(max_low_pfn) to sh_ksyms_32.c

Min_low_pfn and max_low_pfn were used in pfn_valid macro if defined
CONFIG_FLATMEM.  When the functions that use the pfn_valid is used in
driver module, max_low_pfn and min_low_pfn is to undefined, and fail to
build.

  ERROR: "min_low_pfn" [drivers/block/aoe/aoe.ko] undefined!
  ERROR: "max_low_pfn" [drivers/block/aoe/aoe.ko] undefined!
  make[2]: *** [__modpost] Error 1
  make[1]: *** [modules] Error 2

This patch fix this problem.
Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Cc: Kuninori Morimoto <kuninori.morimoto.gx@gmail.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/sh/kernel/sh_ksyms_32.c

@@ -20,6 +20,11 @@ EXPORT_SYMBOL(csum_partial_copy_generic);
 EXPORT_SYMBOL(copy_page);
 EXPORT_SYMBOL(__clear_user);
 EXPORT_SYMBOL(empty_zero_page);
+#ifdef CONFIG_FLATMEM
+/* need in pfn_valid macro */
+EXPORT_SYMBOL(min_low_pfn);
+EXPORT_SYMBOL(max_low_pfn);
+#endif
 
 #define DECLARE_EXPORT(name)		\
 	extern void name(void);EXPORT_SYMBOL(name)