ASoC: dt-bindings: fsl-esai: Remove 'fsl,*' from required list

fsl,fifo-depth have default value 64 in driver(sound/soc/fsl/fsl_esai.c).

fsl,esai-synchronous is flag(bool) type. It doesn't make sense to put flag
type into 'required'.

Fix warning:

arch/arm/boot/dts/nxp/imx/imx6q-sabreauto.dtb: esai@2024000: 'fsl,fifo-depth' is a required property
arch/arm/boot/dts/nxp/imx/imx6q-sabreauto.dtb: esai@2024000: 'fsl,esai-synchronous' is a required property

Signed-off-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20240416-esai_arm_dts_warning-v2-1-879e59c0c3b8@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/fsl,esai.yaml

@@ -67,6 +67,7 @@ properties:
 
   fsl,fifo-depth:
     $ref: /schemas/types.yaml#/definitions/uint32
+    default: 64
     description:
       The number of elements in the transmit and receive
       FIFOs. This number is the maximum allowed value for
@@ -95,8 +96,6 @@ required:
   - clock-names
   - dmas
   - dma-names
-  - fsl,fifo-depth
-  - fsl,esai-synchronous
 
 unevaluatedProperties: false