arm64: dts: add support for S6 based Amlogic BL209

arm64: dts: add support for S6 based Amlogic BL209

Amlogic S6 is an advanced application processor designed for
hybrid OTT/IP Set Top Box and high-end media box applications.

Add basic support for the S6 based Amlogic BL209 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>
Link: https://lore.kernel.org/r/20250317-s6-s7-basic-v1-5-d653384e41f3@amlogic.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>