Most things are already stored in SubdriverArguments and the couple of
things that aren't may change over time and thus should be read again
each time they are accessed, while fetch_header would receive a fixed
copy from pcid.
This commit adds the `get_capabilities` function to `PcidServerHandle`
which returns all of the `Capability`s (raw representation) of the PCI
device.
Signed-off-by: Anhad Singh <andypython@protonmail.com>
bjorn3