drivers: do not repeat the pci config parsing

the pci config is already parsed by pci.cc, and thus does not
need to be parsed again in every driver.
The work left to do in the specific drivers is just to make
sense of the BARs.

Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>
Tested-by: Claudio Fontana <claudio.fontana@huawei.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>