hw/arm/bcm2835: Use object_initialize() on PL011State

hw/arm/bcm2835: Use object_initialize() on PL011State

To be coherent with the other peripherals contained in the
BCM2835PeripheralState structure, directly allocate the PL011State
(instead of using the pl011 uart as a pointer to a SysBusDevice).

Initialize the PL011State with object_initialize() instead of
object_new().

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190507163416.24647-6-philmd@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>