ARM: dts: Add SPI nodes to rk3288

This adds basic SPI nodes to the base rk3288 device tree file.

A few notes:
* It's assumed that most users of the SPI ports are using chip select
  0.  Thus the default pinctrl for the ports enables chip select 0
  (but not chip select 1 on ports that have it).  If a board wants to
  use chip select 1 or wants a GPIO chip select the board should
  override the pinctrl (just like boards can override UART pinctrl if
  they have hardware flow control).
* Since SPI DMA support appears broken and the SPI works fine without
  DMA we don't include the DMA references.  That can come in a later
  change.

Signed-off-by: huang lin <hl@rock-chips.com>
Signed-off-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>