Do not require layered AHardwareBuffers for phones.

Some phones upgrading from older Android versions have gralloc
implementations that will not be updated and do not support the
allocation of layered buffers. Restrict the CTS check that ensures
support for them to standalone VR headsets.

Bug: 116075544
Test: Passes on Pixel 2
Change-Id: Ib8294d2f4e14b58f9410bba6d34c113ad3010a83
2 files changed