drm/vmwgfx: Remove usage of MOBFMT_RANGE

Using MOBFMT_RANGE in the early days of guest backed objects was a major
performance win but that has changed a lot since. There's no more
a performance reason to use MOBFMT_RANGE. The device can/will still
profit from the pages being contiguous but marking them as MOBFMT_RANGE
no longer matters.
Benchmarks (e.g. heaven, valley) show that creating page tables
for mob memory is actually faster than using mobfmt ranges.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Martin Krastev <krastevm@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211206172620.3139754-12-zack@kde.org