i2c: gpio: Run deblock sequence on probe

Add deblock dequence for the I2C bus, needed on some devices. This sequence
is issued once, when probing the driver, and is controlled by DT property,
"i2c-gpio,deblock".

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Heiko Schocher <hs@denx.de>