hw/misc: Add RISC-V CPC device implementation

Add RISC-V implementation of the Cluster Power Controller (CPC) device.
It is based on the existing MIPS CPC implementations but adapted for
RISC-V systems.

The CPC device manages power control for CPU clusters in RISC-V
systems.

This is needed for the MIPS BOSTON AIA board.

Signed-off-by: Chao-ying Fu <cfu@mips.com>
Signed-off-by: Djordje Todorovic <djordje.todorovic@htecgroup.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20260108134128.2218102-9-djordje.todorovic@htecgroup.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>