Search/permit /vendor/${LIB}/hw in sphal namespace

The vulkan runtime loads drivers into the sphal namespace and relies
on them being in the sphal search path so that it doesn't have to
hardcode /vendor/${LIB}/hw.

These paths used to be allowed, but were removed by commit 2498e1b1
because they were believed not to be required. Things didn't break
immediately because the vulkan runtime has a (supposed to be
temporary) fallback to hw_get_module, which loads from
/vendor/${LIB}/hw using absolute paths.

Bug: 123600276
Test: Launch Vulkan app on device with hw_get_module disabled
Change-Id: I07ac43bc9d2d877d8f427058b2d62c62d065c558