1.) Fix an off-by-one in the DVMA space handling, which would make it
possible to allocate one page beyond the end of the DVMA area.
This page was aliased to the first page. Apparently, this bug was
responsible for the trashed nvram/eeprom some people were reporting,
in conjunction with a number of unfortunate coincidences.
2.) Fix broken boundary and and lowaddr calculations.
3.) Fix a memory leak on an error path.
4.) Update a outdated comment to reflect the introduction of IOMMU_MAX_PRE,
make the usage of IOMMU_MAX_PRE more consistent and KASSERT that the
preallocation size is not 0.
5.) Fix a case where an error return was lost.
6.) When signalling an error to the caller by invoking the callback, do
not use a segment pointer of NULL for compatability with existing
drivers.
Also, increase the maximum segment number to 64; it is rather arbitrary,
with the exception of the of the stack space consumed by the segment
array.
Special thanks go to Harti Brandt <brandt@fokus.fraunhofer.de> for
spotting 4 and 5, and testing many iterations of patches.
Pointy hats to: tmm
c5298f4e6c