arm64: dts: qcom: x1e78100-t14s: Add LCD variant with backlight support

arm64: dts: qcom: x1e78100-t14s: Add LCD variant with backlight support

Due to the fact that Lenovo Thinkpad T14s Gen6 is available with both
OLED and LCD, the backlight control differs HW-wise. For the LCD variant,
the panel's backlight is controlled via one of the PWMs provided by the
PMK8550 PMIC. For the OLED variant, the backlight is internal to the
panel and therefore it is not described in devicetree.

For this reason, create a generic dtsi for the T14s by renaming the
existing dts. While at it, add a node name to panel and drop the enable
gpio and pinctrl properties from the panel node. Then add the LCD variant
dts file with the old name and describe all backlight related nodes.

So the existing dts will now be used for LCD variant while for OLED new
dts will be added.

Tested-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
Link: https://lore.kernel.org/r/20250314140325.4143779-3-abel.vesa@linaro.org
Signed-off-by: Bjorn Andersson <andersson@kernel.org>