soc: sophgo: cv1800: rtcsys: New driver (handling RTC only)

soc: sophgo: cv1800: rtcsys: New driver (handling RTC only)

Add driver for Sophgo CV1800 series SoC RTC subsystem. The RTC module
comprises a 32kHz oscillator, Power-on-Reset (PoR) sub-module, HW state
machine to control chip power-on, power-off and reset. Furthermore, the
8051 subsystem is located within RTCSYS including associated SRAM block.

This patch only populates RTC sub-device.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Reviewed-by: Inochi Amaoto <inochiama@gmail.com>
Link: https://lore.kernel.org/r/20250315224921.3627852-3-alexander.sverdlin@gmail.com
Signed-off-by: Inochi Amaoto <inochiama@gmail.com>
Signed-off-by: Chen Wang <unicorn_wang@outlook.com>
Signed-off-by: Chen Wang <wangchen20@iscas.ac.cn>