dt-bindings: mfd: convert mxs-lradc bindings to json-schema

dt-bindings: mfd: convert mxs-lradc bindings to json-schema

Convert the Freescale MXS Low-Resoulution ADC (LRADC) device tree
binding documentation to json-schema.

The clocks and #io-channel-cells properties have also been added; They
are present in the respective SoC DTSI files but were missing from the
old mxs-lradc.txt file.

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20250530160748.2476088-2-dario.binacchi@amarulasolutions.com
Signed-off-by: Lee Jones <lee@kernel.org>