soc: rockchip: Set the proper PWM for rk3288

The rk3288 SoC has two PWM implementations available, the "old"
implementation and the "new" one.  You can switch between the two of
them by flipping a bit in the grf.

The "old" implementation is the default at chip power up but isn't the
one that's officially supposed to be used.  ...and, in fact, the
driver that gets selected in Linux using the rk3288 device tree only
supports the "new" implementation.

Long ago I tried to get a switch to the right IP block landed in the
PWM driver (search for "rk3288: Switch to use the proper PWM IP") but
that got rejected.  In the mean time the grf has grown a full-fledged
driver that already sets other random bits like this.  That means we
can now get the fix landed.

For those wondering how things could have possibly worked for the last
4.5 years, folks have mostly been relying on the bootloader to set
this bit.  ...but occasionally folks have pointed back to my old patch
series [1] in downstream kernels.

[1] https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1391597.html

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

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