I2C: MV64XYZ: Add Device Tree support

Extends the driver to get properties from device tree. Rather than
pass the N & M factors in DT, use the more standard clock-frequency
property. Calculate N & M at run time. In order to do this, we need to
know tclk. So the driver uses clk_get() etc in order to get the clock
and clk_get_rate() to determine the tclk rate. Not all platforms
however have CLK, so some #ifdefery is needed to ensure the driver
still compiles when CLK is not available.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
[wsa: converted some ints to u32 to match signedness]

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>