powerpc/86xx: Add I2C device mappings in DTS for SBC610

Mappings for temperature sensors (adt7461 and lm92) are missing from the
SBC610's DTS file.

Signed-off-by: Martyn Welch <martyn.welch@gefanuc.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>