Implement the PSP's VPL allocation method.

May help some games which hit allocation / free errors.  VPLs are not
common.

May improve performance in games using VPLs heavily, like Pangya.
Correct some vpl allocation logic.

Tricky.  This makes more tests pass, seems right.
Merge pull request #5310 from unknownbrackets/vpl

Track vpl allocation in PSP ram, use similar algorithm to the PSP