sparc/leon3: Fix to put grlib,* devices on sysbus

sparc/leon3: Fix to put grlib,* devices on sysbus

leon3_generic_hw_init() creates a "grlib,ahbpnp" and a "grlib,apbpnp"
sysbus device in a way that leaves them unplugged.

Create them the common way that puts them into the main system bus.
Affects machine leon3_generic.  Visible in "info qtree":

     bus: main-system-bus
       type System
    +  dev: grlib,ahbpnp, id ""
    +    mmio 00000000fffff000/0000000000001000
    +  dev: grlib,apbpnp, id ""
    +    mmio 00000000800ff000/0000000000001000
       dev: grlib,irqmp, id ""

Cc: Fabien Chouteau <chouteau@adacore.com>
Cc: KONRAD Frederic <frederic.konrad@adacore.com>
Cc: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Cc: Artyom Tarasenko <atar4qemu@gmail.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: KONRAD Frederic <frederic.konrad@adacore.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200609122339.937862-22-armbru@redhat.com>
Acked-by: Artyom Tarasenko <atar4qemu@gmail.com>