arm: dts: meson-gxl: fix USB gadget by adding missing nodes for U-Boot

The khadas-vim, khadas-vim2, libretech-ac & libretech-*-pc boards were missing
DT tweak to enable USB gadget.
Add them to their -u-boot.dtsi files and include the right gxl-u-boot.dtsi.

Fixes: a19e8a0f ("arm: dts: meson-gxl: Add USB Gadget nodes for U-Boot")
Reported-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>