sh_eth: add sh_eth_cpu_data::xdfar_rw flag

The GEther-like controllers have writeable RDFAR/TDFAR, on the others
they are read-only or just absent (on R-Car). Currently we are calling
sh_eth_is_{gether|rz_fast_ether}() in order to check if these registers
can be written to, however it would be simpler to check the new 'xdfar_rw'
bitfield in the 'struct sh_eth_cpu_data'...

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/renesas/sh_eth.h b/drivers/net/ethernet/renesas/sh_eth.h
index aa3c451..25c0b1d 100644
--- a/drivers/net/ethernet/renesas/sh_eth.h
+++ b/drivers/net/ethernet/renesas/sh_eth.h
@@ -508,6 +508,7 @@
 	unsigned rpadir:1;	/* E-DMAC have RPADIR */
 	unsigned no_trimd:1;	/* E-DMAC DO NOT have TRIMD */
 	unsigned no_ade:1;	/* E-DMAC DO NOT have ADE bit in EESR */
+	unsigned xdfar_rw:1;	/* E-DMAC has writeable RDFAR/TDFAR */
 	unsigned hw_checksum:1;	/* E-DMAC has CSMR */
 	unsigned select_mii:1;	/* EtherC have RMII_MII (MII select register) */
 	unsigned rmiimode:1;	/* EtherC has RMIIMODE register */