ARM64: dts: rockchip: Change PWM regulators to 300kHz for gru base

ARM64: dts: rockchip: Change PWM regulators to 300kHz for gru base

Apparently the time constant for for the PWM regulator circuit on
gru-based devices is different than EVB.  Let's run at 300kHz which
should make us work well.

BUG=None
TEST=None

Change-Id: I0973f416d026de27908c3ef527c1e9274b967fc8
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-on: https://chrome-internal-review.googlesource.com/254648
Reviewed-by: Stephen Barber <smbarber@google.com>
Tested-by: Doug Anderson <dianders@google.com>