i2c: Move PPC4xx I2C driver into drivers/i2c directory

This patch moves the PPC4xx specific I2C device driver into the I2C
drivers directory. All 4xx config headers are updated to include this
driver.

Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/include/configs/netstal-common.h b/include/configs/netstal-common.h
index 4bed7ae..cb7efe7 100644
--- a/include/configs/netstal-common.h
+++ b/include/configs/netstal-common.h
@@ -42,6 +42,7 @@
  * I2C
  */
 #define CONFIG_HARD_I2C		1	/* I2C with hardware support */
+#define CONFIG_PPC4XX_I2C		/* use PPC4xx driver		*/
 #define CONFIG_SYS_I2C_SPEED		400000	/* I2C speed and slave address	*/
 #define CONFIG_SYS_I2C_SLAVE		0x7F