riscv: Add SOPHGO SOC family Kconfig support

The first SoC in the SOPHGO series is SG2042, which contains 64 RISC-V
cores.

Reviewed-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Chao Wei <chao.wei@sophgo.com>
Signed-off-by: Chen Wang <unicorn_wang@outlook.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>