dt-bindings: serial: Change to reference the kernel-defined serial.yaml

The /schemas/serial.yaml from dt-schema only has the property $nodename,
whereas the kernel-defined /schemas/serial/serial.yaml contains more
useful properties, support for more complex application scenarios.

For example:
1) The property "current-speed" in fsl-lx2160a.dtsi
2) The subnode "bluetooth" in hi3660-hikey960.dts

Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Zhen Lei <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/devicetree/bindings/serial/8250.yaml

···
   - [e-mail]
 
 allOf:
-  - $ref: /schemas/serial.yaml#
+  - $ref: serial.yaml#
   - if:
       anyOf:
         - required:

Documentation/devicetree/bindings/serial/brcm,bcm7271-uart.yaml

···
   - Al Cooper <[e-mail]>
 
 allOf:
-  - $ref: /schemas/serial.yaml#
+  - $ref: serial.yaml#
 
 description: |+
   The Broadcom UART is based on the basic 8250 UART but with

Documentation/devicetree/bindings/serial/ingenic,uart.yaml

···
   - Paul Cercueil <[e-mail]>
 
 allOf:
-  - $ref: /schemas/serial.yaml#
+  - $ref: serial.yaml#
 
 properties:
   $nodename:

Documentation/devicetree/bindings/serial/pl011.yaml

···
   - Rob Herring <[e-mail]>
 
 allOf:
-  - $ref: /schemas/serial.yaml#
+  - $ref: serial.yaml#
 
 # Need a custom select here or 'arm,primecell' will match on lots of nodes
 select:
···
   poll-rate-ms: [ auto-poll ]
   poll-timeout-ms: [ auto-poll ]
 
-additionalProperties: false
+unevaluatedProperties: false
 
 examples:
   - |

Documentation/devicetree/bindings/serial/qca,ar9330-uart.yaml

···
   - Oleksij Rempel <[e-mail]>
 
 allOf:
-  - $ref: /schemas/serial.yaml#
+  - $ref: serial.yaml#
 
 properties:
   compatible:
···
   - clocks
   - clock-names
 
-additionalProperties: false
+unevaluatedProperties: false
 
 examples:
   - |

Documentation/devicetree/bindings/serial/renesas,em-uart.yaml

···
   - clocks
   - clock-names
 
-additionalProperties: false
+unevaluatedProperties: false
 
 examples:
   - |

Documentation/devicetree/bindings/serial/samsung_uart.yaml

···
 unevaluatedProperties: false
 
 allOf:
-  - $ref: /schemas/serial.yaml#
+  - $ref: serial.yaml#
 
   - if:
       properties:

Documentation/devicetree/bindings/serial/sifive-serial.yaml

···
   - Palmer Dabbelt <[e-mail]>
 
 allOf:
-  - $ref: /schemas/serial.yaml#
+  - $ref: serial.yaml#
 
 properties:
   compatible:
···
   - interrupts
   - clocks
 
-additionalProperties: false
+unevaluatedProperties: false
 
 examples:
   - |

Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml

···
   - Rob Herring <[e-mail]>
 
 allOf:
-  - $ref: /schemas/serial.yaml#
+  - $ref: serial.yaml#
 
 properties:
   compatible:

Documentation/devicetree/bindings/serial/st,stm32-uart.yaml

···
   - interrupts
   - clocks
 
-additionalProperties:
-  type: object
+unevaluatedProperties: false
 
 examples:
   - |