Pompom has several sources for its panel. Let's switch it to the
generic edp-panel compatible string to account for this.

This fixes a problem where the panel wouldn't come up on some pompon
devices after commit fb3f43d5 ("drm/panel-edp: Avoid adding
multiple preferred modes"). Specifically, some models of pompom have a
1920x1080 panel which is _very_ different than the 1366x768 panel
specified in the dts. Before the recent panel-edp fix on Linux things
kinda/sorta worked because the panel-edp driver would include both the
hardcoded and probed mode, AKA:

* #0 1920x1080
  60.00 1920 1944 1960 2000 1080 1083 1088 1111 133320
  flags: nhsync, nvsync; type: preferred, driver
* #1 1366x768
  60.00 1366 1406 1438 1500 768 773 778 900 81000
  flags: nhsync, nvsync; type: preferred, driver

...and, at least on ChromeOS, the userspace was consistently picking
the first mode even though both were marked as "preferred". Now that
the Linux driver is fixed we only get the hardcoded mode. That means
we end up trying to drive a 1920x1080 panel at 1366x768 and it doesn't
work so well.

Let's switch over to the generic panel-edp.

Fixes: fb3f43d5 ("drm/panel-edp: Avoid adding multiple preferred modes")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Acked-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Link: https://lore.kernel.org/r/20231213163501.1.I8c20f926d15c9ddc12e423e07df1e89db1105d93@changeidSigned-off-by: Bjorn Andersson <andersson@kernel.org>