Finally fix the bit 17 swizzling code.
Finally fix the bit 17 swizzling code.

- pmap_kremove takes a va and a size, not a va range (unlike pmap_remove,
that gratuitious difference is nothing if not annoying).
- fix a memory leak of the bit 17 bitstring.
- fix the offset calculation when iterating through the dma segments.

Tested by Brandon Mercer, his machine now seems to be rock solid.

Remember kids, if a code path has not been tested fully, it does not work!

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars