drm/vmwgfx: Don't use SVGA_REG_ENABLE in modesetting code.

We should not use SVGA_REG_ENABLE anywhere but in the fifo setup code,
since it controls whether the device is active.

Signed-off-by: Jakob Bornecrantz <jakob@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>