drm/panel: Add Sony Tulip Truly NT35521 driver

It adds a DRM panel driver for Sony Tulip Truly NT35521 5.24" 1280x720
DSI panel, which can be found on Sony Xperia M4 Aqua phone.  The panel
backlight is managed through DSI link.

The driver is built using linux-mdss-dsi-panel-driver-generator[1], and
additionally modeling the 5V control GPIOs with regulators and adding
Backlight GPIO support.

[1] https://github.com/msm8916-mainline/linux-mdss-dsi-panel-driver-generator

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210809051008.6172-3-shawn.guo@linaro.org