gpu: host1x: Stop open-coding of_device_uevent()

There is apparently no reasons to open-code of_device_uevent() besides:
- The helper receives a struct device while we want to use the of_node
  member of the struct device *parent*.
- of_device_uevent() could not be called by modules because of a missing
  EXPORT_SYMBOL*().

In practice, the former point is not very constraining, just calling
of_device_uevent(dev->parent, ...) would have made the trick.

The latter point is more an observation rather than a real blocking
point because nothing prevented of_uevent() (called by the inline
function of_device_uevent()) to be exported to modules. In practice,
this helper is now exported, so nothing prevent us from using
of_device_uevent() anymore.

Let's use the core helper directly instead of open-coding it.

Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Mikko Perttunen <mperttunen@nvidia.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Frank Rowand <frowand.list@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230622213214.3586530-3-miquel.raynal@bootlin.com