hw/riscv: Add helpers for RISC-V multi-socket NUMA machines

hw/riscv: Add helpers for RISC-V multi-socket NUMA machines

We add common helper routines which can be shared by RISC-V
multi-socket NUMA machines.

We have two types of helpers:
1. riscv_socket_xyz() - These helper assist managing multiple
   sockets irrespective whether QEMU NUMA is enabled/disabled
2. riscv_numa_xyz() - These helpers assist in providing
   necessary QEMU machine callbacks for QEMU NUMA emulation

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>
Message-Id: <20200616032229.766089-4-anup.patel@wdc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>