Experimental patch to try to properly clip the range of the memory

Experimental patch to try to properly clip the range of the memory
request to one that's supported by the bridge.  I'm not 100% sure this
is correct, but it makes it easier for the cardbus bridge to allocate
its memory.

Similar code is needed for the I/O range.  Also, I'm not sure if I
should be doing this based on memory or pmemory (but likely should do
it based on some flag that tells us to prefetch or not).

Talked about a long time ago with: msmith