drivers: i2c: Add 10 bit addressing flag to i2c message flags.

This commit adds I2C_MSG_ADDR_10_BITS flag, while keeping
I2C_ADDR_10_BITS for backward compatibility.

I2C_ADDR_10_BITS flag should be removed as soon as all drivers
are modified to use message flag.

Signed-off-by: Mieszko Mierunski <mieszko.mierunski@nordicsemi.no>