dt-bindings: thermal: cooling-devices: Update support for 3 cells cooling device

dt-bindings: thermal: cooling-devices: Update support for 3 cells cooling device

Extend the thermal cooling device binding to support a 3 cells specifier
along with the 2 cells format.

Update #cooling-cells property to enum to support both 2 and 3 arguments.

Fix pwm-fan.yaml to restrict the number of cells to 'const: 2'

Signed-off-by: Gaurav Kohli <gaurav.kohli@oss.qualcomm.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@oss.qualcomm.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Acked-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Link: https://patch.msgid.link/20260526140802.1059293-22-daniel.lezcano@oss.qualcomm.com