Added geteblk_special() to get buffer pages with special control flags

- Fixes emmc support by using a special buffer
- Refactoring memalign functions
- Adds some vm functionality like adding a new page table to a mm struct

Known defects:
Well, geteblk_special() is internally ugly as hell and kernel dynamic
section mapping is a hack. Latter should be fixed by using bitmaps at
least...