apb: remove busA property from PBMPCIBridge state

apb: remove busA property from PBMPCIBridge state

Since the previous commit the only remaining use of the qdev busA property is
to configure the PCI bridge in front of the onboard ebus devices differently
to allow early OpenBIOS serial console access.

Instead we can now manually update the PCI configuration for bridge A in
pci_pbm_reset() and thus completely remove the busA property from the
PBMPCIBridge state.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Artyom Tarasenko <atar4qemu@gmail.com>