As a consequence of the adding IOMMU support to the platform driver,
additional RAM and CAPs are needed for setting up IO page-table
structures.
genodelabs/genode#5002
Instead of allowing the client to set a caching attribute
in the io_mem() call of the device interface, which was
only used to decide in between of the memory being
write-combined or not, remove it from the API.
Instead use the information delivered by the devices ROM,
whether memory from a PCI BAR is prefetchable or not,
to decide whether it is mapped write-combined or not.
Ref genodelabs/genode#4578
