spi: mediatek: add single/quad mode support

Merge series from Leilk Liu <leilk.liu@mediatek.com>:

This series of patches are based on spi for-next, and provide 3 patches
to support MT7986.

Documentation/devicetree/bindings/spi/mediatek,spi-mt65xx.yaml

@@ -53,16 +53,20 @@ properties:
     maxItems: 1
 
   clocks:
+    minItems: 3
     items:
       - description: clock used for the parent clock
       - description: clock used for the muxes clock
       - description: clock used for the clock gate
+      - description: clock used for the AHB bus, this clock is optional
 
   clock-names:
+    minItems: 3
     items:
       - const: parent-clk
       - const: sel-clk
       - const: spi-clk
+      - const: hclk
 
   mediatek,pad-select:
     $ref: /schemas/types.yaml#/definitions/uint32-array