i2c: omap: switch to threaded IRQ support

for OMAP2, we can easily switch over to threaded
IRQs on the I2C driver. This will allow us to
spend less time in hardirq context.

Signed-off-by: Felipe Balbi <balbi@ti.com>
[Trivial formating changes]
Signed-off-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>