drivers/ukbus/platform: Add uk_bus_pf_devmap

drivers/ukbus/platform: Add uk_bus_pf_devmap

Add `uk_bus_pf_devmap()` for mapping device regions. Because of the
current boot flow that initializes the vmmap API after the probing
the interrupt controller - which is required for bringing up secondary
cores - it is not possible to use uk_vma_map_dma() here, so we need to
resort to the low level paging API and map devices 1:1.

Signed-off-by: Michalis Pappas <michalis@unikraft.io>
Reviewed-by: Marco Schlumpp <marco@unikraft.io>
Reviewed-by: Rares Miculescu <miculescur@gmail.com>
Approved-by: Razvan Deaconescu <razvand@unikraft.io>
GitHub-Closes: #1116