hw/intc: riscv_aclint: Add reset function of ACLINT devices

hw/intc: riscv_aclint: Add reset function of ACLINT devices

This commit implements reset function of all ACLINT devices.
ACLINT device reset will clear MTIME and MSIP register to 0.

Depend on RISC-V ACLINT spec v1.0-rc4:
https://github.com/riscv/riscv-aclint/blob/v1.0-rc4/riscv-aclint.adoc

Signed-off-by: Jim Shu <jim.shu@sifive.com>
Reviewed-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20220420080901.14655-5-frank.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>