riscv: Fix to put "riscv.hart_array" devices on sysbus

riscv: Fix to put "riscv.hart_array" devices on sysbus

riscv_sifive_e_soc_init(), riscv_sifive_u_soc_init(),
spike_board_init(), spike_v1_10_0_board_init(),
spike_v1_09_1_board_init(), and riscv_virt_board_init() create
"riscv-hart_array" sysbus devices in a way that leaves them unplugged.

Create them the common way that puts them into the main system bus.
Affects machines sifive_e, sifive_u, spike, spike_v1.10, spike_v1.9.1,
and virt.  Visible in "info qtree", here's the change for sifive_e:

     bus: main-system-bus
       type System
    +  dev: riscv.hart_array, id ""
    +    num-harts = 1 (0x1)
    +    hartid-base = 0 (0x0)
    +    cpu-type = "sifive-e31-riscv-cpu"
       dev: sifive_soc.gpio, id ""

Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Alistair Francis <Alistair.Francis@wdc.com>
Cc: Sagar Karandikar <sagark@eecs.berkeley.edu>
Cc: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Cc: qemu-riscv@nongnu.org
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20200609122339.937862-20-armbru@redhat.com>