DM: I2C: Introduce 'u-boot, i2c-transaction-bytes' property

The 'u-boot,i2c-transaction-bytes' device tree property provides
information regarding number of bytes transferred by a device in a
single transaction.

This change is necessary to avoid hanging devices after soft reset.
One notable example is communication with MC34708 device:

1. Reset when communicating with MC34708 via I2C.

2. The u-boot (after reboot -f) tries to setup the I2C and then calls
force_idle_bus. In the same time MC34708 still has some data to be sent
(as it transfers data in 24 bits chunks).

3. The force_idle_bus() is not able to make the bus idle as 8 SCL
clocks may be not enough to have the full transmission.

4. We end up with I2C inconsistency with MC34708.

This PMIC device requires 24+ SCL cycles to make finish any pending I2C
transmission.

Signed-off-by: Lukasz Majewski <lukma@denx.de>

include/i2c.h

@@ -68,9 +68,11 @@ struct dm_i2c_chip {
  * I2C bus udevice.
  *
  * @speed_hz: Bus speed in hertz (typically 100000)
+ * @max_transaction_bytes: Maximal size of single I2C transfer
  */
 struct dm_i2c_bus {
 	int speed_hz;
+	int max_transaction_bytes;
 };
 
 /*