soc: keystone_serdes: create a separate SGMII SerDes driver

This patch split the Keystone II SGMII SerDes related code from
Ethernet driver and create a separate SGMII SerDes driver.
The SerDes driver can be used by others keystone subsystems
like PCI, sRIO, so move it to driver/soc/keystone directory.

Add soc specific drivers directory like in the Linux kernel.
It is going to be used by keysotone soc specific drivers.

Signed-off-by: Hao Zhang <hzhang@ti.com>
Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>
diff --git a/include/configs/k2hk_evm.h b/include/configs/k2hk_evm.h
index 45bd72d..034cbfd 100644
--- a/include/configs/k2hk_evm.h
+++ b/include/configs/k2hk_evm.h
@@ -41,4 +41,7 @@
 #define CONFIG_KSNET_NETCP_V1_0
 #define CONFIG_KSNET_CPSW_NUM_PORTS	5
 
+/* SerDes */
+#define CONFIG_TI_KEYSTONE_SERDES
+
 #endif /* __CONFIG_K2HK_EVM_H */