hw/riscv: microchip_pfsoc: Connect 5 MMUARTs

Microchip PolarFire SoC has 5 MMUARTs, and the Icicle Kit board
wires 4 of them out. Let's connect all 5 MMUARTs.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <1598924352-89526-7-git-send-email-bmeng.cn@gmail.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>