Broken direct assignment of MMIO regions smaller than 4K

[parthy]

There are several places in the direct assignment code where it fails because e.g. a size of 2KiB gets rounded down to 0:

in_range returns false:
https://github.com/TUD-OS/NUL/blob/master/vancouver/model/directmem.cc#L35
https://github.com/TUD-OS/NUL/blob/master/vancouver/model/pcidirect.cc#L330

mapping is of size 0:
https://github.com/TUD-OS/NUL/blob/master/vancouver/model/pcidirect.cc#L333

[blitz]

Fixed in seoul. Needs to be backported.