move arch/sh/lib/io.o to obj-y

EXPORT_SYMBOL's in lib-y considered harmful:

<--  snip  -->

...
  MODPOST 1837 modules
ERROR: "__raw_readsl" [drivers/ssb/ssb.ko] undefined!
ERROR: "__raw_writesl" [drivers/ssb/ssb.ko] undefined!
ERROR: "__raw_writesl" [drivers/net/smc91x.ko] undefined!
ERROR: "__raw_readsl" [drivers/net/smc91x.ko] undefined!
ERROR: "__raw_writesl" [drivers/net/3c59x.ko] undefined!
ERROR: "__raw_readsl" [drivers/net/3c59x.ko] undefined!
...
make[2]: *** [__modpost] Error 1

<--  snip  -->

Reported-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>