riscv: dts: sophgo: Move riscv cpu definition to a separate file

As sg2000 and sg2002 can boot from an arm a53 core, it is not
suitable to left the riscv cpu definition in the common peripheral
header.

Move the riscv related device into a separate header file, so the
arm subsystem can reuse the common peripheral header.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Link: https://lore.kernel.org/r/20250430012654.235830-3-inochiama@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>