i2c: core: Map OF IRQ at probe time

I2C clients instantiated from OF get their IRQ mapped at device
registration time. This leads to the IRQ being silently ignored if the
related irqchip hasn't been proved yet.

Fix this by moving IRQ mapping at probe time using of_get_irq(). The
function operates as irq_of_parse_and_map() but additionally returns
-EPROBE_DEFER if the irqchip isn't available, allowing us to defer I2C
client probing.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>