arm: dts: k3-*-r5: Add MPU clock in clocks property

arm: dts: k3-*-r5: Add MPU clock in clocks property

MPU clock had been missing. Distinguish multiple clocks with clock-names
and add MPU clock as well.

Link: https://software-dl.ti.com/tisci/esd/latest/5_soc_doc/j721s2/clocks.html#clocks-for-a72ss0-core0-device
Signed-off-by: Manorit Chawdhry <m-chawdhry@ti.com>
Reviewed-by: Aniket Limaye <a-limaye@ti.com>