riscv: dts: microchip: update peripherals in icicle kit device tree

Assorted minor changes to the MPFS/Icicle kit device tree:

- enable mmuart4 instead of mmuart0
- remove sifive pdma
- split memory node to match updated fpga design
- move stdout path to serial1 to avoid collision with
        bootloader running on the e51

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>