Fit ps8640 driver into runtime power management framework:

First, break _poweron() to 3 parts: (1) turn on power and wait for
ps8640's internal MCU to finish init (2) check panel HPD (which is
proxied by GPIO9) (3) the other configs. As runtime_resume() can be
called before panel is powered, we only add (1) to _resume() and leave
(2)(3) to _pre_enable(). We also add (2) to _aux_transfer() as we want
to ensure panel HPD is asserted before we start AUX CH transactions.

Second, the original driver has a mysterious delay of 50 ms between (2)
and (3). Since Parade's support can't explain what the delay is for,
and we don't see removing the delay break any boards at hand, remove
the delay to fit into this driver change.

In addition, rename "powered" to "pre_enabled" and don't check for it
in the pm_runtime calls. The pm_runtime calls are already refcounted
so there's no reason to check there. The other user of "powered",
_get_edid(), only cares if pre_enable() has already been called.

Lastly, change some existing DRM_...() logging to dev_...() along the
way, since DRM_...() seem to be deprecated in [1].

[1] https://patchwork.freedesktop.org/patch/454760/Signed-off-by: Philip Chen <philipchen@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
[dianders: fixed whitespace warning reported by dim tool]
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211028105754.v5.1.I828f5db745535fb7e36e8ffdd62d546f6d08b6d1@changeid