Convert binding doc ads7846.txt to yaml format.
Additional change:
- add ref to touchscreen.yaml and spi-peripheral-props.yaml.
- use common node name touchscreen.
- sort ti properties alphabetically.
- sort common properties alphabetically.
- sort compatible string alphabetically.
- remove vcc-supply from required list.
- deprecated ti,x-min, ti,y-min

Fix below warning: arch/arm64/boot/dts/freescale/imx8mm-var-som-symphony.dtb: touchscreen@0:
	ti,x-min: b'\x00}' is not of type 'object', 'array', 'boolean', 'null'
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20240826162302.960732-1-Frank.Li@nxp.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>