cmd_eeprom: make it possible to define the used i2c bus

A SoC like the i.MX6 supports more then one i2c bus. In oder to be
able to use the eeprom command add a new define to specify the
i2c bus to use. If CONFIG_SYS_I2C_EEPROM_BUS is not defined there
is no functional change, else a call to i2c_set_bus_num(..) is
done before calling i2c_read(..) and i2c_write(..).

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Acked-by: Stefano Babic <sbabic@denx.de>
diff --git a/common/cmd_eeprom.c b/common/cmd_eeprom.c
index 29f0f1f..e9904cd 100644
--- a/common/cmd_eeprom.c
+++ b/common/cmd_eeprom.c
@@ -161,6 +161,9 @@
 #if defined(CONFIG_SPI) && !defined(CONFIG_ENV_EEPROM_IS_ON_I2C)
 		spi_read (addr, alen, buffer, len);
 #else
+#if defined(CONFIG_SYS_I2C_EEPROM_BUS)
+		i2c_set_bus_num(CONFIG_SYS_I2C_EEPROM_BUS);
+#endif
 		if (i2c_read(addr[0], offset, alen - 1, buffer, len))
 			rcode = 1;
 #endif
@@ -339,6 +342,9 @@
 		/* Write is enabled ... now write eeprom value.
 		 */
 #endif
+#if defined(CONFIG_SYS_I2C_EEPROM_BUS)
+		i2c_set_bus_num(CONFIG_SYS_I2C_EEPROM_BUS);
+#endif
 		if (i2c_write(addr[0], offset, alen - 1, buffer, len))
 			rcode = 1;