pwm: pwm-mediatek: Add support for MediaTek Helio X10 MT6795

The MediaTek Helio X10 MT6795 SoC has 7 PWMs: add a compatible string
to use the right match data.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>