In order to facilitate understanding, rockchip SPI controller IP design
looks similar in its registers to designware. But IC implementation
is different from designware, So we need a dedicated driver for Rockchip
RK3XXX SoCs integrated SPI. The main differences:

- dma request line: rockchip SPI controller have two DMA request line
  for tx and rx.

- Register offset:
                  RK3288        dw
  SPI_CTRLR0      0x0000        0x0000
  SPI_CTRLR1      0x0004        0x0004
  SPI_SSIENR      0x0008        0x0008
  SPI_MWCR        NONE          0x000c
  SPI_SER         0x000c        0x0010
  SPI_BAUDR       0x0010        0x0014
  SPI_TXFTLR      0x0014        0x0018
  SPI_RXFTLR      0x0018        0x001c
  SPI_TXFLR       0x001c        0x0020
  SPI_RXFLR       0x0020        0x0024
  SPI_SR          0x0024        0x0028
  SPI_IPR         0x0028        NONE
  SPI_IMR         0x002c        0x002c
  SPI_ISR         0x0030        0x0030
  SPI_RISR        0x0034        0x0034
  SPI_TXOICR      NONE          0x0038
  SPI_RXOICR      NONE          0x003c
  SPI_RXUICR      NONE          0x0040
  SPI_MSTICR      NONE          0x0044
  SPI_ICR         0x0038        0x0048
  SPI_DMACR       0x003c        0x004c
  SPI_DMATDLR     0x0040        0x0050
  SPI_DMARDLR     0x0044        0x0054
  SPI_TXDR        0x0400        NONE
  SPI_RXDR        0x0800        NONE
  SPI_IDR         NONE          0x0058
  SPI_VERSION     NONE          0x005c
  SPI_DR          NONE          0x0060

- register configuration:
  such as SPI_CTRLRO in rockchip SPI controller:
    cr0 = (CR0_BHT_8BIT << CR0_BHT_OFFSET)
        | (CR0_SSD_ONE << CR0_SSD_OFFSET);
    cr0 |= (rs->n_bytes << CR0_DFS_OFFSET);
    cr0 |= ((rs->mode & 0x3) << CR0_SCPH_OFFSET);
    cr0 |= (rs->tmode << CR0_XFM_OFFSET);
    cr0 |= (rs->type << CR0_FRF_OFFSET);
  For more information, see RK3288 chip manual.

- Wait for idle: Must ensure that the FIFO data has been sent out
  before the next transfer.
Signed-off-by: addy ke <addy.ke@rock-chips.com>
Signed-off-by: Mark Brown <broonie@linaro.org>