[Intel-gfx] Change TTM from using pfn to bytes

[Christian König]

Hi guys,

this is an extract from Amar's earlier patch set with quite some
re-ordering, bug fixes and separating changes into smaller patches.

Background is that we want to use GEM/TTM to manage all kind of
resources which most are not accounted in pages but rather bytes or even
arbitary units (hw blocks for example).

Sending this out so that the Intel CI can take another look at it.

Regards,
Christian.