drm/vmwgfx: Port vmwgfx to arm64

This change fixes all of the arm64 issues we've had in the driver.
ARM support is provided in svga version 3, for which support we've added
in previous changes. svga version 3 currently lacks many of the
advanced features (in particular 3D support is lacking) but
that will change in time.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210505035740.286923-7-zackr@vmware.com