i2c: designware_i2c.c: Add support for the "i2c probe" command

i2c: designware_i2c.c: Add support for the "i2c probe" command

i2c_probe() is changed to reinit the i2c bus upon read failure.
This is naturally the case upon i2c bus probing.

Also, some printf messages upon read failure are removed. As they
would interfere with the "i2c probe" command.

Additionally, i2c_set_bus_speed() now returns 0, so that the
"i2c speed" command can be used.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Amit Virdi <amit.virdi@st.com>
Cc: Vipin Kumar <vipin.kumar@st.com>