drm/vmwgfx: Switch to exclusively using GEM references

drm/vmwgfx: Switch to exclusively using GEM references

Currently we use a combination of TTM and GEM reference counting which is
cumbersome. TTM references are used for kernel internal BOs and operations
like validation. Simply switching the ttm_bo_(get|put) calls to their
GEM equivalents is insufficient as not all BOs are GEM BOs so we must set
the GEM vtable for all BOs even if they are not exposed to userspace.

Suggested-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Ian Forbes <ian.forbes@broadcom.com>
Reviewed-by: Zack Rusin <zack.rusin@broadcom.com>
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250131200321.193939-1-ian.forbes@broadcom.com