arm64: dts: meson: add thermal zones to meson gx devices

Adapt and update current VIM2 thermal zones support so that zones are
available on all meson GXBB/GXL/GXM devices - similar to changes made
for G12A/G12B/SM1 devices.

Suggested-by: Nick Xie <nick@khadas.com>
Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/1584328854-28575-1-git-send-email-christianshewitt@gmail.com