arm64: dts: add support for A5 based Amlogic AV400

arm64: dts: add support for A5 based Amlogic AV400

Amlogic A5 is an application processor designed for smart audio
and IoT applications.

Add basic support for the A5 based Amlogic AV400 board, which describes
the following components: CPU, GIC, IRQ, Timer and UART.
These are capable of booting up into the serial console.

Signed-off-by: Xianwei Zhao <xianwei.zhao@amlogic.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20240401-basic_dt-v3-5-cb29ae1c16da@amlogic.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>