Vendor & layer paths on Android

[Jeremy-Kemp]

Currently the common default path for Vendor ICD or layer files is /system/vendor/Khronos/OpenCL/vendors

If Android's Soong build system is used to install ICD and/or layer files on Android (e.g. by using prebuilt_root), a custom directory under /system/vendor cannot be created. As such, it would be beneficial if the common path could be updated for Android to support users leveraging Soong for these files.

/system is also simply a symlink to /vendor so that prefix could be removed at the same time.

An initial suggestion allowing Soong's prebuilt_etc (where subdirectories can be created) rule to be leveraged would be to set the paths to /vendor/etc/opencl/{drivers,layers} either as the default Android path, or as a build option to maintain compatibility with any shipping configurations.