Move libvr_hwc-hal and vr_hwc into system_ext

they are not a part of the system according to
generic_system.mk.

Bug: 173538619
Bug: 167689596
Test: presubmit
Signed-off-by: Roman Kiryanov <rkir@google.com>
Change-Id: I00fad53e29794130983534f7e9ebc05ac09cc1d8