Switch port I/O based PCI config space access to memory-mapped IO. The
base address of the PCI configuration space is acquired by mapping the
ACPI ROM and reading the first <bdf> node. An exception is thrown if the
first <bdf> node is not for PCI domain zero or if multiple <bdf> nodes
exist. This is to reduce complexity and also because multiple PCI
domains are rare.
The PCI configuration space is accessed via I/O mem dataspace which is
created in the platform_drv root and then passed on to the PCI session,
device components and finally to the actual PCI config access instances.
The memory access code is implemented in a way to make it work with Muen
subject monitor (SM) device emulation and also general x86 targets. On
Muen, the simplified device emulation code (which works also for Linux)
always returns 0xffff in EAX to indicate a non-existing device.
Therefore, EAX is enforced in the assembly templates.
Fixes#2547
