powerpc/85xx: TQM8548: DTS file fixes and cleanup

Due to the missing compatible property for the SOC, the MPC I2C buses are
not found any more. This patch fixes this issue. Furthermore it corrects
the name of the SOC node and adds the missing I2C node for the RTC.

Signed-off-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>