Add support for reading the extended PCIe configuration space
Adds support for reading the PCIe extended configuration space, by reading the MCFG table provided by the new
acpi: scheme. If the scheme is available, which it is if and only if the "acpi" cargo feature is enabled for the kernel,
pcid will never call
out, and solely rely on DMA.
Nothing that only resides in the extended configuration space is currently used, but it might be beneficial to implement AER at some point.