hw/intc: Upgrade the SiFive CLINT implementation to RISC-V ACLINT

hw/intc: Upgrade the SiFive CLINT implementation to RISC-V ACLINT

The RISC-V ACLINT is more modular and backward compatible with
original SiFive CLINT so instead of duplicating the original
SiFive CLINT implementation we upgrade the current SiFive CLINT
implementation to RISC-V ACLINT implementation.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Message-id: 20210831110603.338681-3-anup.patel@wdc.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>