ARM: dts: Change I2C2 and I2C3 to 400KHz for LogicPD Torpedo DM3730 devkit

When used with the Logic PD development kit, this makes the I2C buses match
the BSP released by Logic PD.

Signed-off-by: Adam Ford <adam.ford@logicpd.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>