Activate QPF2 font support in INTEGRITY

QPF2 fonts are so far not supported on Qt for INTEGRITY, probably because INTEGRITY does not support mapped files using mmap call.

This is a major drawback from my perspective, since there is (at least to my knowledge) no publicly available QPF1 font generator and the provided QPF1 fonts are ugly (=unusable).

By replacing the mmap calls by fopen, QPF2 fonts can be used on INTEGRITY (at the cost of physical memory).

See the attached patch for the necessary changes.