arm64: dts: meson-gxm-khadas-vim2: fix Bluetooth support

- Remove serial1 alias
- Add support for uart_A rts/cts
- Add bluetooth uart_A subnode qith shutdown gpio

Fixes: b8b74dda ("ARM64: dts: meson-gxm: Add support for Khadas VIM2")
Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>