powercap: dtpm: Simplify with of_machine_get_match_data()

powercap: dtpm: Simplify with of_machine_get_match_data()

Replace open-coded getting root OF node, matching against it and getting
the match data with new of_machine_get_match_data() helper.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patch.msgid.link/20251112-b4-of-match-matchine-data-v2-9-d46b72003fd6@linaro.org
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>