sh_eth: uninline sh_eth_{write|read}()

Commit 3365711d

 ("sh_eth: WARN on access to a register not implemented in
in  a particular chip") added WARN_ON() to sh_eth_{read|write}(), thus making
it  unacceptable for these functions to be *inline* anymore. Remove *inline*
and move the functions from the header to the driver itself. Below   is our
code economy with ARM gcc 4.7.3:

$ size drivers/net/ethernet/renesas/sh_eth.o{~,}
   text	   data	    bss	    dec	    hex	filename
  32489	   1140	      0	  33629	   835d	drivers/net/ethernet/renesas/sh_eth.o~
  25413	   1140	      0	  26553	   67b9	drivers/net/ethernet/renesas/sh_eth.o

Suggested-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>