drm/vmwgfx: Copy DRM hash-table code into driver

Besides some legacy code, vmwgfx is the only user of DRM's hash-
table implementation. Copy the code into the driver, so that the
core code can be retired.

No functional changes. However, the real solution for vmwgfx is to
use Linux' generic hash-table functions.

v2:
	* add TODO item for updating vmwgfx (Sam)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211129094841.22499-3-tzimmermann@suse.de