dt-bindings: mfd: x-powers,axp152: Document AXP717

The X-Powers AXP717 is a PMIC used on some newer Allwinner devices.
Among quite some regulators it features the usual ADC/IRQ/power key
parts, plus a battery charger circuit, and some newly introduced USB
type-C circuitry.
Like two other recent PMICs, it lacks the DC/DC converter PWM frequency
control register, that rate is fixed here as well.

Add the new compatible string, and add that to the list of PMICs without
the PWM frequency property.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Tested-by: Ryan Walklin <ryan@testtoast.com>
Link: https://lore.kernel.org/r/20240310010211.28653-3-andre.przywara@arm.com


Signed-off-by: Lee Jones <lee@kernel.org>