Optimize VM handling a bit more

[Christian König]

Hi everyone,

Especially on Vega and Raven VM handling is rather inefficient while creating PTEs because we originally only supported 2 level page tables and implemented 4 level page tables on top of that.

This patch set reworks quite a bit of that handling and adds proper iterator and tree walking functions which are then used to update PTEs more efficiently.

A totally constructed test case which tried to map 2GB of VRAM on an unaligned address is reduced from 45ms down to ~20ms on my test system.

As a very positive side effect this also adds support for 1GB giant VRAM pages additional to the existing 2MB huge pages on Vega/Raven and also enables all additional power of two values (2MB-2GB) for the L1.

This could be beneficial for applications which allocate very huge amounts of memory because it reduces the overhead of page table walks by 50% (huge pages where 25%).

Please comment and/or review,
Christian.