riscv: dts: spacemit: define a SPI controller node

riscv: dts: spacemit: define a SPI controller node

Define a node for the fourth SoC SPI controller (number 3) on the
SpacemiT K1 SoC.

Enable it on the Banana Pi BPI-F3 board, which exposes this feature
via its GPIO block:
  GPIO PIN 19:  MOSI
  GPIO PIN 21:  MISO
  GPIO PIN 23:  SCLK
  GPIO PIN 24:  SS (inverted)

Define pincontrol configurations for the pins as used on that board.

(This was tested using a GigaDevice GD25Q64E SPI NOR chip.)

Reviewed-by: Yixun Lan <dlan@gentoo.org>
Signed-off-by: Alex Elder <elder@riscstar.com>
Signed-off-by: Guodong Xu <guodong@riscstar.com>
Link: https://lore.kernel.org/r/20260502-spi-spacemit-k1-v10-3-f412e1ae8a34@riscstar.com
Signed-off-by: Yixun Lan <dlan@kernel.org>