arm64: dts: qcom: sc7280: eDP for herobrine boards

Add eDP support to herobrine boards, splitting up amongst the
different files as makes sense. Rationale for the current split of
things:
* The eDP connector itself is on qcard. However, not all devices with
  a qcard will use an eDP panel. Some might use MIPI and, presumably,
  someone could build a device with qcard that had no display at all.
* The qcard provides a PWM for backlight that goes to the eDP
  connector. This PWM is also provided to the board and it's expected
  that it would be used as the backlight PWM even for herobrine
  devices with MIPI displays.
* It's currently assumed that all herobrine boards will have some sort
  of display, either MIPI or eDP (but not both).
* We will assume herobrine-rev1 has eDP. The schematics allow for a
  MIPI panel to be hooked up but, aside from some testing, nobody is
  doing this and most boards don't have all the parts stuffed for
  it. The two panels would also share a PWM for backlight, which is
  weird.
* herobrine-villager and herobrine-hoglin (crd) also have eDP.
* herobrine-hoglin (crd) has slightly different regulator setup for
  the backlight. It's expected that this is unique to this board. See
  comments in the dts file.
* There are some regulators that are defined in the qcard schematic
  but provided by the board like "vreg_edp_bl" and
  "vreg_edp_3p3". While we could put references to these regulators
  straight in the qcard.dtsi file, this would force someone using
  qcard that didn't provide those regulators to provide a dummy or do
  an ugly /delete-node/. Instead, we'll add references in
  herobrine.dtsi.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220426124053.v2.1.Iedd71976a78d53c301ce0134832de95a989c9195@changeid