hw/dma: sifive_pdma: Don't run DMA when channel is disclaimed

hw/dma: sifive_pdma: Don't run DMA when channel is disclaimed

If Control.run bit is set while not preserving the Control.claim
bit, the DMA transfer shall not be started.

The following result is PDMA tested in U-Boot on Unleashed board:

=> mw.l 0x3000000 0x0                      <= Disclaim channel 0
=> mw.l 0x3000000 0x1                      <= Claim channel 0
=> mw.l 0x3000004 0x55000000               <= wsize = rsize = 5 (2^5 = 32 bytes)
=> mw.q 0x3000008 0x2                      <= NextBytes = 2
=> mw.q 0x3000010 0x84000000               <= NextDestination = 0x84000000
=> mw.q 0x3000018 0x84001000               <= NextSource = 0x84001000
=> mw.l 0x84000000 0x87654321              <= Fill test data to dst
=> mw.l 0x84001000 0x12345678              <= Fill test data to src
=> md.l 0x84000000 1; md.l 0x84001000 1    <= Dump src/dst memory contents
84000000: 87654321                               !Ce.
84001000: 12345678                               xV4.
=> md.l 0x3000000 8                        <= Dump PDMA status
03000000: 00000001 55000000 00000002 00000000    .......U........
03000010: 84000000 00000000 84001000 00000000    ................
=> mw.l 0x3000000 0x2                      <= Set channel 0 run bit only
=> md.l 0x3000000 8                        <= Dump PDMA status
03000000: 00000000 55000000 00000002 00000000    .......U........
03000010: 84000000 00000000 84001000 00000000    ................
=> md.l 0x84000000 1; md.l 0x84001000 1    <= Dump src/dst memory contents
84000000: 87654321                               !Ce.
84001000: 12345678                               xV4.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20210927072124.1564129-2-bmeng.cn@gmail.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>