dts: riscv: microsemi-miv: define CLINT

The SoC seems to embed a CLINT instance, defined at 0x44000000.

Ref. https://github.com/Mi-V-Soft-RISC-V/platform/blob/main/


miv_rv32_hal/miv_rv32_hal.h

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>