hw/riscv: sifive_u: Connect a DMA controller

SiFive FU540 SoC integrates a platform DMA controller with 4 DMA
channels. This connects the exsiting SiFive PDMA model to the SoC,
and adds its device tree data as well.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <1598924352-89526-17-git-send-email-bmeng.cn@gmail.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

hw/riscv/Kconfig

@@ -22,6 +22,7 @@ config SIFIVE_U
     select CADENCE
     select HART
     select SIFIVE
+    select SIFIVE_PDMA
     select UNIMP
 
 config SPIKE