drm: panel: add Khadas TS050 panel driver

This add support for the Khadas TS050 1080x1920 5" LCD DSI panel designed to work
with the Khadas Edge-V, Captain, VIM3 and VIM3L Single Board Computers.
It provides a MIPI DSI interface to the host, a built-in LED backlight
and touch controller.

The init values was taken from the vendor source tree, comments were added to the
know values but most of the init table is undocumented.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
[narmstrong: call drm_panel_remove if mipi_dsi_attach fails]
Link: https://patchwork.freedesktop.org/patch/msgid/20201204081949.38418-3-narmstrong@baylibre.com