i2c: config: Move SYS_I2C_DW to Kconfig

This patch moves all appearances of CONFIG_SYS_I2C_DW from the config
header to the defconfig files.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Heiko Schocher <hs@denx.de>
Cc: Alexey Brodkin <abrodkin@synopsys.com>
diff --git a/configs/spear320_usbtty_defconfig b/configs/spear320_usbtty_defconfig
index 9e41253..de75b17 100644
--- a/configs/spear320_usbtty_defconfig
+++ b/configs/spear320_usbtty_defconfig
@@ -6,5 +6,6 @@
 CONFIG_CMD_DHCP=y
 CONFIG_CMD_MII=y
 CONFIG_CMD_PING=y
+CONFIG_SYS_I2C_DW=y
 CONFIG_NETDEVICES=y
 CONFIG_ETH_DESIGNWARE=y