arm64: dts: qcom: pm660l: Add LPG node

The Light Pulse Generator describes a hardware block responsible for
displaying colors and patterns on an RGB LED (usually used for [battery]
status and notifications), and drive PWM signals for general-purpose
(ie. backlight) LEDs.  The availability and usage of the individual
channels differ per board and is hence left for individual platform DTs
to configure.

Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
[bjorn: Dropped #address/size-cells]
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220511190718.764445-3-marijn.suijten@somainline.org