Add basic SPI support for SOPHGO SG2042 SoC

Merge series from Zixian Zeng <sycamoremoon376@gmail.com>:

Implemented basic SPI support for SG2042 SoC[1] using
the upstreamed Synopsys DW-SPI IP.

The way of testing can be found here [2].

Signed-off-by: Zixian Zeng <sycamoremoon376@gmail.com>
---
Changes in v6:
- patch 1: Apply Krzysztof's tag.
- patch 2: Adjust enum to alphabetical order.
- Link to v5: https://lore.kernel.org/r/20250422-sfg-spi-v5-0-c7f6554a94a0@gmail.com

Changes in v5:
- patch 1: New patch merges all vendors fall back to snps,dw-apb-ssi into one entry
- Link to v4: https://lore.kernel.org/r/20250407-sfg-spi-v4-0-30ac949a1e35@gmail.com

Changes in v4:
- Adjust the order of spi nodes.
- Place the binding after Renesas.
- Fix the description issues of patches.
- Link to v3: https://lore.kernel.org/r/20250313-sfg-spi-v3-0-e686427314b2@gmail.com

Changes in v3:
- Remove the spi status on sg2042-milkv-pioneer board.
- Remove clock GATE_CLK_SYSDMA_AXI from spi. [3]
- Create dt-binding of compatible property.
- Replace the general compatible property with SoC-specific in dts.
- Link to v2: https://lore.kernel.org/r/20250228-sfg-spi-v2-1-8bbf23b85d0e@gmail.com

Changes in v2:
- Rebase v1 to sophgo/master(github.com/sophgo/linux.git).
- Order properties in device node.
- Remove unevaluated properties `clock-frequency`.
- Set default status to disable.
- Link to v1: https://lore.kernel.org/r/20250228-sfg-spi-v1-1-b989aed94911@gmail.com

Link: https://github.com/sophgo/sophgo-doc/blob/main/SG2042/TRM/source/SPI.rst [1]
Link:
https://lore.kernel.org/all/CAKyUbwXqg13Ho7QHw8vV2W6OcObphwhQ8HUrZMDNBxrVxLmdug@mail.gmail.com/
[2]
Link: https://github.com/sophgo/sophgo-doc/blob/main/SG2042/TRM/source/clock.rst#clock-tree [3]

---
Zixian Zeng (3):
      spi: dt-bindings: snps,dw-apb-ssi: Merge duplicate compatible entry
      spi: dt-bindings: snps,dw-apb-ssi: Add compatible for SOPHGO SG2042 SoC
      riscv: sophgo: dts: Add spi controller for SG2042

 .../devicetree/bindings/spi/snps,dw-apb-ssi.yaml   | 19 ++++++----------
 arch/riscv/boot/dts/sophgo/sg2042.dtsi             | 26 ++++++++++++++++++++++
 2 files changed, 33 insertions(+), 12 deletions(-)
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base-commit: 8ffd015d
change-id: 20250228-sfg-spi-e3f2aeca09ab

Best regards,
--
Zixian Zeng <sycamoremoon376@gmail.com>